I'm between 2 and 4 myself (voted for 4). I had no issues with the previous forum and personally don't really see a great benefit [yet] of the new format. Adding features to the previous forum would have been fine with me. Having said that, I'm not completely opposed to the new AMASS either, it will just take some getting used to. The biggest struggle is the fact that it is different than any other forum - I'm a member of about 6-8 different forums that I visit and use on a pretty regular basis and they all use a very similar setup and structure - whether it's phpBB, vBulletin, etc.
Sure, I get that there have been users on POTN that use Nikon, Fuji, whatever... and that has been the case for a while. Yes, I get that this was never a Canon ONLY place, but it was very Canon-centric - that's why I joined here and not somewhere else. I shoot Canon and want to be amongst the largest amount of others who do as well. Based on the current user base, I think it will likely remain that way, but I do think the forum will also get watered down quite a bit with the new setup. I'll give two examples of where I expect to see this...
1) I frequently visit the Flash and Studio Lighting section. Sure, lights are mostly generic, unless you are talking about Canon Speedlites. However, today the MAJORITY of users who post there today are shooting with Canon bodies. So when the question comes up about supportability with ETTL triggers, it's pretty standard to suggest those Canon supported products. I foresee this changing, with more shooters from the other brands joining in with questions about flashes, triggers etc that work with their brand. This waters down the Canon-centric part I mentioned above.
Heck, I'm on a specific forum to the model car I drive - not just the Brand/Manufacturer, the specific model. It's powerful to be able to find specific information like that.
2) The Classifieds area. Again, sure, there are non-Canon items listed, but the large majority of items posted today are Canon centric. I foresee this changing quite a bit where it will be more common to see a lot more items from the other brands listed. I don't own an Olympus, so I don't care to see those items. Today it's easy to browse past the (maybe) one per page, but that's changing...
I get that there is ongoing work for the Classifieds area to. I haven't read into it specifically, but it sounds like you may be able to search for specific item - that's great if I'm looking for something specific; I used to handle that by going to the section then searching for the specific item within the section. However, I also just like to generally browse what's selling too - again, Canon-centric items. So, I'm hoping there will be some good filtering options so I can get rid of all the stuff that I don't care to see.