Clearly, the multipool is not the only factor. Blackcoin has brought some innovation to the market(the multipool), has gathered an enthusiast community and comes with no premine and no inflation because it is POS.
It has inflation but is very low in total 1% yearly inflation.
I don't know. I think is fixed in the code.
Maybe making a fork this can be "adjusted".
What would be the market conditions to change the inflation rate?!