One of the options RaidSummon has is right click frames to add someone to the list
https://raw.githubusercontent.com/isitLoVe/RaidSummon/master/pics/RaidSummon_RightClick.PNG

Very handy and one feature I'm missing especially when people aren't saying 123 :P

Yea, that is something I will get to at some point.

Would be nice to have. As a workaround, I just have a macro I can use to manually add people. Target them via raid frames, then
/p !SS add %t
(It seems to mess up sometimes due to some addon of mine when the person has a raid target icon, but I rarely find myself needing to manually add people with raid target icons, so ymmv.)

Actually, here's a better macro that doesn't suffer from the raid target icon problem:
/run SendChatMessage('!SS add '..UnitName("target"), "PARTY")