There's also the question of limited resources. I've only really got time for about an hour or two's worth of work on RTC a week - I could either spend that time making versions backwards compatible, or spend it making the next version better...
As advance warning I've already had to make some big changes to the underlying format for the next version (codename V0.16 - catchy eh - shhh, don't tell anyone

so the versions won't be backwards compatible...
On the plus side though, the changes allow you to create your own new graphics (not just over-rides) and add some new features needed for CSB...