For new deployments, we try to go with ElasticXL/VSNext as much as possible, this is where the development will be for years to come and better get used with the new tech as soon as possible in real-world situations.
This being said, we have customers who insist on deploying proven technologies because all the changes are too much at the same time when you add features like UPPAK, P/E cores and so on.
Obviously, a migration tool would greatly help with the technological adoption, we seldom have the opportunity to completely tear down and recreate production clusters.