Very nice! I like supporting those options, even though I don't see a stock 80mm fan FlexATX being viable, I'll explain that in a moment.
It makes a lot of sense to enable support for the HDPLEX PSU, though, I can see quite a few people wanting that. What's the maximum fan thickness for the 80mm fan on the PSU?
So, about the 80mm fan thing. We already discussed that it's not viable to let a PSU OEM manufacture a FlexATX PSU with an 80mm fan already mounted, it would simply cost too much and the MOQ would be too high.
In theory, having vent slots in the top and mounting points to allow the user to mount an 80mm fan sounds like a swell idea, but there are multiple problems with that.
Firstly, if the PSU manufacturer does it, they have to completely retest it for compliance with international regulations, else it is pretty much illegal to sell. Again, high cost, high MOQ. Additionally, it could be that the PSUs 40mm fan isn't sufficient to cool some parts inside the PSU with the added vent slots, so that has to be tested as well.
Secondly, if you let a metalshop do it, and sell it with the PSU, you would have to test that stuff yourself or get a company to do it. You could of course just sell it anyway, but if something goes wrong, just ONE thing for ONE person, even if they didn't open the unit, you could be fucked. End of business. And even if you test it, you will not be able to advertise this functionality in any way.
This is not a DCDC board we're talking about, this stuff can kill people if something goes wrong.
The only way I see that this is viable is to include the support for this in the case and allow people that really wanna do it to mod the PSU themselves.
Maybe, just maybe it would be possible to let a metalshop do the alternative top and sell that as a standalone product. That's the only way I can see this work out, and even then you should consider contacting a lawyer to make sure what you're doing won't bit you in the end. If that was the plan I apologise for the wall of text, but I just don't want to see a good project like this turn out bad for you just because you were a little bit too careless.