At this point I can't see a new RPG Maker coming out because there was a lot of investment on the "VX" line, with the official VX assets followed by VX Ace (that was compatible) and its arising contents too. Doesn't seem logical, on the perspective of a company, to launch a completely new line of softwares that would be twice as better as the old ones but not compatible with the content available (considering the investment on that, which now is stronger than ever).
On my Humble opinion, a new RPG Maker could be very welcome IF they make it in a level where it can actually compete with other engines of the same kind on the market today. I'm not even going to focus on specific problems like the terrible tileset managing (improved from VX to Ace but still worse than XP's), but other limitations like the lack of malleability and portability. Some things are very tricky to do when they shouldn't be, and I'm talking about changing the game's keyboard settings, native resolution/aspect ratio and such (not to mention the Windows-only support). We all know that RPG Maker is intended to make just one type of game, different from engines like Unity and Construct2, but even so, the lack of some of these features makes the engine feel VERY outdated. On top of this, the EULA restrictions blocks some malleability that can't be proportioned only through RGSS, restricting the use of patches or plugins that could make a huge difference for the user base. Also, I remember of testing the IGM when it was out and it wasn't very far from RPG Maker on these aspects, either.
If you want to make a 3D game, I suggest to study it and look for other engines like Unity (which haves a free version). By the way, I personally experienced RPG Maker 2 and 3 for PS2 once after seeing people talking about them, so I wanted to check by myself and see if they were as bad as they talked about. Despite of RPG Maker 2 having great customization (someone made a golf game on it apparently), it was extremely tricky and tiring to use. RPG Maker 3 was just bad - it had some interesting ideas and tools like the various terrain and climate settings, but other than that it wasn't worth at all for a big amount of reasons like inconsistent material, extremely limited resource usage, boring battle system and the list goes on. Maybe a PC version could work really well though, as it wouldn't have the hardware limitations of a console version, but even so A LOT of work would have to be put on it to make it as worth as Unity, Cry or Unreal.
Anyway, I'm not expecting a new version of RPG Maker at the moment. But if it was announced that a new one is coming out, I would hope for everything I said before: more malleability, portability, support to user created plugins and extensions, basically everything the other engines on the market haves + all the good stuff that was abandoned on older versions. Make the "RPG" concept more broad would also be very pleasant, with options to make different kinds of turn based combat systems and maybe even enough support to create action RPGs. A 3D RPG Maker for PC could be interesting, but I doubt this is something that would happen and even if it happened, it's unlikely it would be so good as the specific engines that already exists at the moment.