Yes, the upgrade path from MultiChain 1.0 to 2.0 will be very smooth. First, MultiChain 2.0 will continue supporting a chain created in 1.0, without that chain's protocol being upgraded. Second, you'll have the option of upgrading the chain's protocol, once all the nodes are running MultiChain 2.0, using the built-in upgrade mechanism (which works just like a hard fork). And finally there is complete API stability, with a small number of exceptions explained in the "Incompatible API changes" section here:
https://www.multichain.com/developers/multichain-2-0-preview-releases/