I agree upgrading Grails has been painful in the past(pre 3.0), but more for underlying Spring/dependency upgrades/changes. Most of the upgrade pains I've seen from Grails itself have been from people using bad practices, but there was usually a config flag to get that bad practice to still work, like auto wiring in Domain classes. As for hiring, I see that it's always hard to hire good people, who are proactive, want to make the code base better, and want to learn new things. If you can find people with those characteristics, who also already know Java/Spring. Learning Grails is not a big stretch. Just opinions based on my experience.