The entire code for the engine is in the js folder of each project - so, technically speaking, anything is
possible if you're sufficiently fluent in JavaScript and spend enough time and effort to code it.
However, this is
very different from what RPG Maker is designed to do, so it would require a lot of work to create.
There are a variety of plugins intended to recreate a square-grid tactics game, and I have never heard of one that was feature complete. You may want to consider a game maker that is designed to make tactics games in the first place, as you would start off much closer to your end goal.
Do you think the upcoming Unite version would be easier to do it on?
No. The base structure of the engine, the kind of game it's designed to make, is the same.
The style of the assets may be a bit different, and the language used to code it is different, but it will be just as much work to undo what the game comes with and remake what you want.