One of the biggest problems with rolling out a new LMS is getting your teachers on board with having to move all their data to a new system. By adopting the Common Cartridge Standard, we can make this transition easier.
https://www.imsglobal.org/activity/common-cartridge
This will also help teachers be able to share their work with other teachers, which would be a great benefit as well.
Seamless integration can only be accomplished through standards and cooperation. Proprietary systems are not necessarily why new systems are used - efficiency, customer service and satisfaction is.