Here is a list of what stuff that isn't an original idea for a TDM.
Knife tdm.
spear tdm.
identical bases on both sides but with different colors, tdm.
cube-y land, tdm.
idiots vs handicaps vs zombies, tdm.
Dogfight, tdm.
Jail rp, tdm. (Obviously is one big death match)
City rp, tdm. (Obviously is one big death match)
Tf2, tdm.
Halo, tdm.
Mw2, tdm.
Anything with tier tactical or guns that reload, tdm.
Gears of war, tdm.
And so on.
If you want to see something original for an example, stop on my server whenever I host any TDMs.
(Usually never but I never had any complaints for them being unoriginal)