The Baikal Miner X10 for example, started with X11/Quark/Qubit Algorythm
Since Release they also added Myriad-Groestl and Skein and they announcend that 2 more will come soon.
For the fact, that they used an ASIC Chip which is "only" designed for X11/Quark/Qubit, they added much more Algos.

I dont think that's impossible to add more algos to the D3, but if Bitmain will do that....