Re the Brummbar, Tamiya has been going through there very old IV based kits over the last few years and new tooling them.
The Jagdpanzer IV was effective their 3rd gen chassis of the IV, thinking there should be a StuG IV out from them within the next 2 years going on this pattern.
Tamiya have their 2nd gen chassis for the IV H/J, Wirbelwind & Mobelwagen, maybe after then have finished with the StuG, they will look at other older kits to new-tool (M3 Lee/Grant/M3 Light) or be radical, and do something like different version of what the already have, say a L48 version of the Jagdpanzer IV