It looks like it might make a decent host. The shelf is more narrow than the previous HK94, so as a sear host a SEF housing would need to be fitted to the new dimensions. The bolt carrier appears to be semi auto with the trip milled off however it doesn't look like they made any effort to block a full auto carrier from being used like they did with the SP5K. So, the carrier could be welded up or a factory auto carrier substituted. As pointed out, the rear sight drum would be problematic with a stock attached but that is easily rectified. The barrel is threaded 1/2x28 which has a lot more options than the 1/2x32 Navy barrel that my MP5 has.
I'd like to take this opportunity to hijack the thread and do another PTR shout out. I recently acquired a PTR 9KT which is their MP5K or SP89 clone. It is sear ready. And by sear ready I mean drop in your pack and shoot. On my first trip to the range with it I took my Fleming sear equipped pack and dropped it into the PTR SEF housing. I put on my HK marked Choate made MP5K stock and put the pins in. They were a little tight but they did line up and the stock fit snugly with no wobble. An Allen wrench is required to remove the factory PTR handguard however the bolt is threaded into the handguard and the hanger is made to normal specs so the vertical K grip fit and pinned into place with no problem. Of course the PTR comes from the factory with a full auto bolt carrier.
The first trip to the range I burned through about 200 rounds with zero malfunctions. The second trip I exceeded 300 rounds and again, zero malfunctions. I'm totally amazed that PTR can put out a clone of this quality that runs straight out of the box. Time will tell if they will hold up but I can tell you that I intend to find out.
This past weekend I had a mishap with the G3 host. It's a Springfield SAR3 imported from Greece. I've had it since the early 90's. I've lost count of how many cases of 7.62x51 surplus I've put through it. Enough that the wear and tear finally took it's toll about two weeks ago. It jammed so I pulled the charging handle back to clear it. The brass had somehow migrated into the trigger group so I pulled the stock and pack off to clear it. The brass fell out and I put it all back together and attempted to reload it. Releasing the charging handle sent it forward but the bolt didn't move. Perplexed I disassembled it again and found the issue. The German surplus G3 bolt carrier had broken in half. NICE! That one is out of commission. I took the rifle home and put the semi carrier back in it. It hasn't been in there in years. While cleaning up the rifle I noticed something else. The barrel was basically a smoothbore for the first third of its length. It looks like a cross between a polygonal barrel and a gain twist rifled barrel. But the darn thing still shoots great! Once I get a new bolt carrier I'll start running it again. In the meantime I have a PTR 51 and G3K clone to expend .308 slugs. Those are both working extremely well.