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....
and I believe that is more possible that we all know..
but think about, whoever find a way to mine diff algo will never be an idiot and share it/make it public. why? easy.. profit!
if all D3 users would jump on "new algo" the profit will destroy, no?
so we have to continue life^^ and buy other asics and do/hope the best