The Belgian Revolution still happens at some point due to the religious, cultural and language barriers that existed between the Netherlands and Flanders and between Flanders and Wallonia (plus Luxembourg, but they were basically happy with anyone in charge).
Hmmm... 'Culture' is a very vague term, but what religious and linguistic border was there between Flanders and the other catholic parts of the Netherlands? Let's not forget that catholicism is still today the largest denomination in the Netherlands, and has always been predominant in North Brabant and many places in Zeeland, Gelderland and Holland proper – none of which seemed to have any inclination towards revolt in 1830 (Limburg beint the exception). If there's any religious difference, then it's more in the sense that the church in Belgium wasn't used not to be the sole religious player.
Also, even in the Belgian case, it should not be forgotten that a significant part of the clergy was Orangist – because of its conservative/legitimist view on politics.
Weren't most of the southern industrialists Orangists as well? Hell, until 1850 there was a very active Belgian counter-movement that basically wanted to restore the united kingdom. Anyhoo, the 19th century was pretty shit for the Netherlands. Any chance this pod would make it better?
Indeed, Orangism as a political force in Belgium only began to wane in the 1840's – even the official Dutch recognition of Belgian independence in 1839 did not stop Orangist to attempt coups at late as 1841. As a political movement, 1848 was the real blow to it – with political power now largely in the hands of a Dutch political elite which never really was that much interested in the 'lost cause' as Willem I & Willem II, and with Willem II fearing that orangist agitation in Belgium could lead to the 1848 revolutionary wave hitting The Hague harder than it did.
So in 1880 or whenever, most Belgians aren't gonna go "Well, that doddering old King Frederik whupped our grandfathers' arses 50 years ago, obviously we don't deserve the right to autonomy/independence." Its a Poland-style problem: however long you keep these guys under the thumb, they aren't going to suddenly become Dutch, and the next major conflict that the Netherlands gets involved in will pretty much definitely spark an internal conflict between the Seven Provinces and the rest.
National identities are not set in stone: they fluctuate according to political circumstances, even Henri Pirenne would aknowledge that. Sure, there was a certain potential for the existing Belgian proto-identity evolving into a strong national identity in 1830, but a lot can happen between 1830 and 1880, or even 1848. Of course, the amount in which a state can 'manipulate' or at least influence the national feeling of its citizens, is dependent on a lot of factors – which is why I don't think the analogy with Poland as a very apt one: Poland differed in both language as well as religion from Russia, factors which are absent or less prominent in the Belgian/Dutch case. Antwerp and Breda are both Dutch (Brabantic)-speaking, catholic cities, which were in that respect equally as different from Amsterdam and The Hague. The North and the South had continued their literary exchange after 1585, so written language was mostly the same, though spelling did give some minor (but symbolically important) problems – the North had introduced the Siegenbeek spelling in 1804, when Napoleon already ruled in the South.
Also, Poland had a much more pronounced pre-existing state identity.
So I do think that The Hague had a lot more room for manoeuvering and winning the Battle for the Belgian Heart. E.g. a Thorbecke(-like) constution could weaken Belgian separatism, as it might satisfy the liberal opposition against Willem I in Belgium. Thorbecke's constitutional revision also ended the privileged position of the Dutch Reformed Church (one of the least fortunate aspects of the UKN), which – together with the reestablishment of the episcopal hierarchy in 1853, would at least ease relationship with the RCC. And there's a lot of ways of co-opting members of the Belgian elite to you.
In fact, everything indicates hat loyalism remained the dominant opinion amongst Belgium's elite (industrials, nobility, administrators) until well after 1830, with the general population probably being lukewarm or indifferent to the whole question, but easily manipulated by both sides in case of economic crises – as effectively happened in 1830.
The resilience of non-elite organism can also be seen in late 19th century socialist writings. Not only is '1830' frequently cursed in the writings of the labour movement's intellectual and political leaders, mainly from Brussels and Ghent (Bertrand, De Paepe, even Anseele), organist themes pop up in labour movement related songs from both Ghent and Liège(!). Of course, some of that may also be part of an 'invented tradtition'. (Those who read Dutch might be interested in checking Maarten van Ginderachter's recent works, as is Els Witte's recent book about Belgian organism between 1830 and 1850)
So while it is indeed likely that there will be some kind of Belgian revolt, but the absence of Willem II's buffoonery might be one of those elements that will prevent it ending in the breaking away of the Southern Netherlands. I doubt, however, that this absence itself would suffice. (France not becoming involved would be nice, oh, and Poland, did you really have to revolt at the same time?). And if the revolt is ended, something will have to change in order for it not to be repeated again.
A minor thing: Willem II dying in Waterloo would of course make his 'Watterloo hero' cult more popular than it was in OTL.
