I would not a sort of mini-TF for those who might have limited time or would rather not play in a large team for some reason. More like a story arc. Some good story-telling can be had there I think.

Oh man, I loved Task Forces. After the first few years, all I did was create a character, level him to 11 in the Atlas Park sewers, then run Positron's Task Force, then I think Synapse, and one after another until I hit 50. I even ran Doctor Quarterfield's Task Force once. Only once. Took 9 hours, and we only lost one member of our 8 person team. Poor guy's wife made him leave at around the 7 or 8 hour mark, when we were so close. Didn't even have any real boss at the end. 25 missions, mostly the same thing three times in a row, then another mission three times in a row.

I loved them as tests of endurance, though Dr. Q was more punishing than it had to be. I'd love to have a range of them, from short ones that are easy to find a team to do, to longer ones that will take a bit more time and fewer people are willing to do, then the hardcore stuff, like a string of missions that could take 8 hours and you'll have to find the most die hard players to do it.

The only Trials I remember are the Eden Spire Trial and the Abandoned Sewer Trial, which were weird, covered a very short range of like 3 levels, and most people had no idea existed because the game never told you about them. You just had to know to get a team together in the right level range, go to an obscure zone and click on a totally random person standing near a dock or something. Man, that was weird stuff.

I like both task-forces and flashpoints.

i love long team building missions. the more coordination needed the happier i am.
i also like short and sweet story missions. "Go do this, thanks here is your reward"

the reward per hour should be equal between the two. So if I have a lot of playtime that day i can do a really long task-force.
if my playtime is short i can do a flashpoint. my rewards look about the same after 1 hour.
once I do say.. 3 flashpoints I unlock 'spawn super flashpoint' which lets me set a super flashpoint mission (everyone in group must have a super flashpoint mission available) and the flashpoint is equal to the reward level of the last mission in a task-force.

this lets players and groups who have less time per day still save up and go do a mission with a big reward, without invalidating the big reward missions that "hardcore" players can grid out in an 8 hour stretch.