The problem is if the full holes are there then I feel they should have grommets to cover them up for people who aren't using them. But that's another item to the BOM and while they're not super expensive or anything, it's not an insignificant price either and I think they're ugly and very few people will use the holes.
I was thinking partial cutouts that users could finish cutting out themselves, though Joshua is opposed to that. So we haven't decided for sure yet.
Partial cutouts are a bad idea when the piece is powerdercoated, and it will feel like those cheapo thin-steeled cases where all the PCIe brackets have to be removed by yourself. You want to avoid any association with that, people are already sceptical of steel, so you need to show them that steel does not equate bad quality.
I don't think you'd have to include rubber grommets. Just having holes there doesn't really hurt. If it really bugs you, add them as an accessory option, so people who want them covered can pay an additional 5 bucks or so to get grommets that fit 100% of the time.
If the rear bracket is still replaceable in the current design, you could make a simple design for a single flat-piece bracket that has the proper cutouts and put it available for download. Than anyone can have it made somewhere or even make it themselves.
Ah, I had forgot about that. The plan is indeed to post dimensions of the rear plate for people to make their own.
This is a great idea and I love that you'll be doing it, but I think the stock option should support as many configurations as possible. If someone wants to go the extra mile to make their build even cleaner, then they could always get a new back cover made without the holes.
Doing it this way around seems more consumer-friendly to me than to require anyone who wants to use the M1 res to also cut a new back cover. Remeber, we're talking about the back of the case here!