How about Elgg team do there update in 3 type just like how Linux & Ubutu do there update..

1) LTS releases (Log Term Support Release)

2) New Release (with 6 months or 2 months of support)

3) Beta Release

Now the new releases will be helpful for new elgg users while the LTS will be helpful for Old elgg users. now New release will have frequent update while the LTS just security updates. Now when the LTS has an update it should have the best of the New release say if new release is some where 2.0 the LTS will be at 11.1 so that the Old websites will have a flexible update. I stress that the elgg team consider this so that much of the community get benefited from this.