I know that Aternos tries everything to be able to implement new plugins.
Dynmap is one of the best plugins out there and deserves a place on Aternos.
It would be a great miracle if Aternos can be added.
Maybe if you talk to the creator, something can be done to add it to Aternos.
It is a complicated thing, but perhaps, something could be done.
I hope, at least, soon, either Dynmap or other alternatives will arrive.