Excellent news! I've seen far more of these little twin vans in the UK than the bogie version modelled by Dapol, at least in the period I can remember.
What is the rationale behind them? They seem very similar to two normal continental Habbins vans (equivalent to VGA) permanently coupled. Surely that creates extra construction and maintenance costs compared to a single bogie wagon? Seems odd we don't really see many single LWB 4 wheel vans in the UK, when they are really common on the mainland, yet we do get these.
I'll definitely order some - I'm slightly surprised you've announced these before delivering that many of the previous models though. I've got several 321s, a 92, and some container flats all on pre-order ...
Still, these make a natural pairing with the 92 - good joined up thinking!
In addition to the information above about loading, my understanding is that at the time (mid 80s) there were grants available to encourage the use of bigger bogie wagons, however UIC descriptions only refer to "2-axle" or "4-axle" wagons. By splitting the brake gear across the wagons Duewag and Cargowaggon were able to argue that the twins were, in effect, a single wagon and qualified for the grants, while at the same time maximising capacity.
Mike has largely answered your point about timings, but in addition I would add that we have held back from any announcements at Model Rail Scotland or York but felt, with the Pendolinos now well into production, the 00 TEAs getting underway, the 92, KFA and Class Bs very close and clear progress made on the HOAs and 321 the time was right to begin the next wagon.
And, as you identified, the progress on the 92 was also a factor in this decision.