Only BMD knows about their plans
My guess is that they won't release an ATEM Mini with SDI. But it's very likely that they will release a Television Studio HD replacement (the small rackmount unit) with the same engine / electronics as the ATEM Mini Extreme. This will more than likely again have half of it's inputs as SDI ports. This does of course not have a control surface.
They might also give the ATEM Television Studio Pro HD an update with the same engine / electronics as the Extreme. This all seems very feasible. Possibly with a design refresh to bring it inline with the 2 M/E and 4 M/E Advanced Panels.
I also expect the other rackmounted ATEM 4M/E, 2M/E and 1M/E models to get an update (hopefully soon, looking at buying a 2M/E this year
) but these will more likely be based on the same engine as the Constellation but then limited to 4K, less ports, etc... Also the Television Studio Pro 4K might get this update.
But who knows if or when...