One of the truly great things abnout Gamera is that his character fits quite comfortably in either absurdist surreal whacked-out stuff like his Showa films OR straight up dark 'n' gritty, adult-slanted adventures like the Heisei trilogy. As others have voiced, I'm also fine with whatever direction they chose. Just don't make it some dumbo comedy nudge-nudge crock, like Guilala's "return" from a few years back. Ack.
If they resurrect an old foe, I'm very partial to Jiger, since it was a clear female opponent and it was probably the best looking quadraped kaiju ever realized on screen from any studio, plus it had some great set pieces and the kids actually served a narrative purpose, instead of just standing around in short-shorts cheering - although they did do that a bit towards the end.
Guiron would be cool to see re-imagined. I would picture him as some sort of cyborg abomination, like Gigan. Barrugon is cool, but kind of hard to make work if they tried to make a "serious" movie. Anyhow, this is some ecouraging news indeed!