I'm unsure how somebody could continually troll groups, after running it once they would be marked as having seen in so they wouldn't have the option to lock.
Some things SE could think about
:
1.) When the new person (s) finish the scene all people are allowed to exit as they wish
2.) The reward would justify the wait, meaning the tomestone bonus could equal or beat the 'tomestones per hour' of average speedrun.
3.) Instance timer doesn't tick down when in cutscene.
4.) Cutscene has a max time allotted before people are able to bypass the lock.
Many more.
I hadn't gone into detail since these are things that would come up during player/SE testing, not really my/our job to brainstorm for them.
I personally don't like the 'checkbox' for new/experienced since it divides the pool of players who are ultimately looking to do the same run.