Eh, it's debatable whether most enemies are actually stationary. They do move during their turn, it's just the turn-based abstraction that makes them look like they're standing still and getting shot at.
Automatic sniper rifles are a bit silly, yes. But AS Val exists, and so do scoped machine guns. Hathcock's record was with an M2, for that matter.
'Sniper' and 'designated marksman' are more of a doctrinal thing. You can certainly have your DM use 0.25-MoA bolt actions and have snipers creep closer and use one of the plethora of modern sub-MoA semi-auto rifles with rapid follow-ups.
Anyway, in terms of this proposal, there's really not much of a difference between a 'sniper rifle' and a 'DMR'. Both have scopes, both are long-range precision weapons used mainly against 'soft' targets.
Incidentally, that's where the actual draw of the semi-auto is. Not range or whatever, you were almost always going to use a full-power round anyway (and semis are worse for those than bolt actions). Rather, it's the rapid follow-ups and multi-target shots that are the draw, compared to bolt actions. Well, I suppose nowadays it might be shooting at drones, too.
Precision semi-autos are far from rare, even in military contexts. The US Army moved from the M24 to the M110 and then an HK417 variant, for crying out loud.
40+ distance itself is not the issue, its interaction with sight range is the thing to consider. If you have open desert or arctic terrain, you can shoot from one end of a 40x40 or even bigger map to the other. I see that you're a fellow sniper enjoyer.
The numerical data are interesting. While not quite what you envisioned, it's not too badly off.
I too would like more fire mode customisation, but I'm not holding my breath. Getting typed hangars would be a major move forward and more useful to many people. And there's all the other stuff on the devs' todo lists.