Sending virtual hugs.
Yes, cross-platform on mobile doesn't sound like a good idea. In fact, I can't recall any game developer that has done that before, they usually have a separate version that is completely different running on mobile, there are so many differences in terms of hardware, software and how you control and interact with it.
Multiplayer could limit them from doing more advanced things too, like we saw in The Sims 4, even if multiplayer games are able to run pretty well side by side with a single player game these days. The only thing that we have heard now is that they are looking for ways to people to collaborate with each other, like building and sharing, and let's hope it stays like that.
They have the opportunity to make their next game into something really good, open world mechanics, textures, graphics have come a long way and it would be quite sad if they don't make use of it but instead spend their resources on trying to get the game to run on a mobile phone and trying to get people to play their game in multiplayer.