However, not a single blockchain platform allows migrating of one blockchain to another blockchain as a fully functional sidechain.

 This problem creates a doubt over the sustainability of a blockchain developed by small group of members or unknown group".

 At least until now, I have not encountered anything.

Can I use any coin other than IFUM for exchange? If so, what coin limit?

The opposite view on the future of electronic money funds comes from the prediction of some experts that bitcoin prices may fluctuate more strongly this year.
Ari Paul, chief investment officer at BlockTower Capital, expects bitcoin prices to fall to $ 4,000 or $ 30,000 in 2018.
One of the reasons experts think that bitcoin price increases are more investors believe that they will make a big profit from the next split. When bitcoin developers decide to implement a system upgrade, investors will receive an equal number of isomers.
It is possible that the predictions of many investors psychological instability and financial stress in the family.