Here's some examples of Deathmatch gamesmodes we all would like to see and that aren't hard to implement:

• normal dm

• random guns dm

• pistol only dm

• team dm

• open server drop in / drop out dm

If you have any other ideas suggest them in the comments I guess. Of course would a custom workshop / player created dm be the best option but that is probably more difficult to implement in the game than a couple modes like these.