Talks about Flemish independence and consequentially Belgian dissolution is nothing new. Pro-independence parties consistently win majorities in Flanders. At the same time negotiations to form federal government take more and more time and increasingly have to include pretty much every single anti-independence party from both left and right to have a majority and make it work somehow. However, such a broad compromise government cannot achieve much, leaving country in never ending impasse. All the while debts keep growing and nothing is getting done.
However, dissolution of Belgium would rise several important issues that has to be addressed somehow. Even if Flanders secede or unite with Netherlands, what is going to happen with Wallonia, Brussels and that small German speaking region. Obviously, it is better to address them before rather than after the dissolution.
Brussels
While issue of Flanders and Wallonia mostly concerns only local residents, the Brussels is not so simple. Brussels is a de-facto capital of European Union and as such its continued functioning is important for every member of the European Union.
As European Union ever grows larger and more powerful, Brussels too keeps growing bigger and bigger. Outer suburbs of the capital already reached out of its designated capital region into the surrounding Flemish Brabant and now border Wallon Brabant as well.
To make sure Brussels can continue to grow and fulfil its role as European capital it needs space. Thus, in the event of Belgian dissolution it needs much more territory than its designated capital territory provides it.
To that end Brussels should be united together with all or most of Brabant province, both Flemish and Wallon Brabants. That will give Brussels enough room to grow and function as a city state and a European capital. Actual borders can be adjusted to include or exclude other important areas, for example a FN Herstal arms factory in Liege Province. To keep border with Germany and Luxembourg even the whole Liege province can be made part of Brussels city state or turned into a separate nation.
Greater Brussels city state should continue to be bi-lingual or maybe even include other languages of the EU as official, particularly large ones such as English and German. The name of this state can be either Brussels, Brabant, or even European Capital State. It should assume legal continuity from original Belgium, possibly shared with European Union as whole. It can be its own sovereign state or even a pan European Union condominium, where sovereignty for the area is ultimately vested in European Union itself.
European Union sovereignty over the Greater Brussels arrangement can strengthen European Union and make it much more empowered on international stage. Much like with the US federal government's District of Columbia, it will give EU a territory with a complete federal control, not shared with any member states. It will also allow European Union to have its own army by taking over the Belgian one.
Flanders
Some in Netherlands propose a union between Flanders and Netherlands. Popularity of this idea is low in Flanders itself, however. Nonetheless this arrangement has several advantages over the independent Flanders.
To begin with it will allow Flanders to continue its membership in European Union without need to re-apply or work out some complex arrangements. It will also save Flanders trouble of creating its own Armed force. Finally, it will shield Flanders from hostile actors in Russia and China who would try to undermine the new state, by promoting pro-Russian puppet candidates.
One might argue that such arrangement will not change much for Flanders. However, the root issue with Flemish independence movement was unwillingness ot subsidize much more impoverished Wallonia. Union with Netherlands does solve just that, as Netherlands is one of the wealthiest states in Europe, thus Flanders would not be the net donor of the union but rather net beneficiary. The second issue was language and here there is no problems at all. Both Netherlands and Flanders speak Dutch, unlike the French speaking Wallonia. In general, there is much more cultural similarity between the two. Finally name Flanders has poor reputation due to being the same as that of certain character from popular American sitcom The Simpsons. A country with such name might struggle to get foreign investment.
In case of the union with Netherlands, Flanders may keep all or most of their powers as a regional autonomy. That will make transition even smoother. Actual powers of the Flemish government can even be increased, even though
Benefits of the Union with Netherlands so outweighs the outright independence, that perhaps this option should be the only alternative to continuation of Belgium with no option for outright independence.
Alternatively, Flanders can indeed become fully independent member of the EU and NATO. Some provisional arrangements have to be implemented to make sure the transition is a smooth one and there is no disruption to European Union or NATO. Security would be particularly important issue here as countries like Russia could try to use transition to damage European security.
Wallonia
Wallonia is by far the easiest to solve part of Belgium. Wallons do not want independence; however, some want to unite with France. Many Wallons dislike even increasing presence of Dutch language and want to promote French language as the only one in the country.
Because of that union with France is a simple solution that serves their aspirations. Sure, Wallonia has huge public dept, but France is not a county that will pass on territorial expansion, even if it has to shoulder the debts of its new territorial possessions, Wallonia's population is but a fraction of French so annexation will not impact French finances in any significant way.
German Speaking Area
Small German speaking area in the far east of Belgium can be given to Germany. That will somewhat offset growth of France at expense of Wallonia.
Conclusion
Despite some opposition to Belgian dissolution, support for this option is strong and ever growing. It is much better to arrange a cohesive transition plan and carry it through than wait until Flanders just declares unilateral independence and plunges not only Belgium but the whole EU into chaos and instability.