If none of the above applies I fear people will be more frustrated than
feeling helpful by forcing them to use java 11 and instead will stick at
older tycho releases.
Maintaining Tycho against Java 8 and 11 is expensive. Look at the Git history, there were several patches that were just produced to deal with Java 8/11 differences. Those patches take time, energy, resources..., that is not spend on other more profitable work.
Let's just say it: people who don't want to migrate to newer releases are slowing down the whole industry and are often not the ones the most to the common parts. I don't get why we should behave so nicely with them to slow down our own work and participate to this "let's not migrate" anti-pattern.
There are a lot of valuable improvements in Java 11, which we can for sure not use if we stick to Java 8, but at some point, if we don't try to move forward, we don't really adopt better code, better practices, and ultimately we also fail at innovating ourselves.
So yes, maybe some people will stick to older Tycho versions, but that's their issue, not the one of the Tycho project itself. People who put constraints like "I want this to work on Java 8" have to pay the price of this constraint; they'll have to invest manpower or money to provide/find support for their older version (and more manpower or money in open-source support is actually a good thing) since the community support will just be dropped in favor of the current and future releases.
So, to be more explicit: does any of the current Tycho code contributor have real need to retain Java 8 support?