So these are being designed and produced at the same time with the ATX case?
Let me explain,
The ATX one is a part of X-ICMBs project (Refer here:
X-ICMBs Will start first), base on LegoFab V3, if I start this project (X-ICMBs) people who back can select any case model with that price (There are many case model in X-ICMBs project,I will show after done website, ATX-Munteman is one, this MATX is also can be made by LegoFab V3 with a bit different).
X-ICBMs's case use same structure, long price range, easy to produce, can bring any case to any one, so people will feel that is is not unique.
This MATX design in this thread is different with X-ICBMs models, it's for some one like a unique model. Hard to produce, So I may consider to make prototype same time with ATX one.
Is the bottom panel vented so that single GPU user can add fans or radiator if they want? Is it correct that there is dual mounting of PSU?
There are vent hole on bottom panel, you can add fan or rad if you run only 1 GPU. There 2 or 3 PSU mounting point, depend which PSU/Rad you selected. The third point is in bottom side for Flex PSU option.