Maybe, we'll have the option that, when we place 2 exhibita next to each other, we have the option to connect them to be 1 large exhibit
I think being able to make the 'shell' of the exhibit invisible would be enough for me to be honest. Seems like it would be a lot less work for the devs than adding in a system to merge exhibits together, the animals would still behave in exactly the same way, but we could make it appear as though the exhibits are a lot more varied.
For example, in paul78's image below your post, you could have the true 'exhibit' portion in the middle (with the box and glass set to 'null'), and use construction glass, rocks etc to make it appear as though the whole area is one larger exhibit. Or you might even be able to sneak multiple exhibits into there, and blend them together with building pieces. I don't know, a little off topic perhaps.
On DLC predictions, I think it's impossible to make a line with one point. Before the aquatic pack, I'd have said that the sun bear is a surefire indication of an Asia pack, as all the packs up to that point had been continents (ok, the arctic isn't technically a continent, but it was all animals from a specific area of the world). The introduction of a biome/behavior based pack in the aquatic pack means the next one is very difficult to predict, but I think whatever it ends up being will potentially be an indication of the plan going forward. If it is Asia/Southeast Asia (I mean, a purely Indonesian pack would be difficult enough to condense down to 4 animals), that would suggest continents/regions are the norm, with occasional deviations like aquatic. If it turns out to be 'jungle' or 'arboreal' or something, that would suggest to me that the coming packs will be a lot more varied and difficult to predict.
There we go, far too many words in order to say 'dunno'.