How about this: a relatively short flight (20 minutes-ish) from a limiting airfield to a large airport. On gear retraction, one you get a gear unsafe condition. When trying to extend the gear again, still unsafe, one main gear won't come down. Wx moderate (say 3000m vis and cieling around 1000' or so). Diversion airfield around 40 minutes beyond destination, this is company base with heavy maintenance, but wx is marginal (say 1500m and 400' perhaps). Marginal amount of extra fuel, say 15 min.
So:
-Deal with normal procedures (ie not engine failure on takeoff...)
-Deal with the unsafe gear in due time (unsolvable - stays unsafe).
-What does the crew do? Continue to destination or go directly to base (which is also the alternate?)
-When trying to extend the gear again, do they do it early in anticipation of problems, or at a normal time, setting the stage for a go-around?
-Is a flyby visual inspection considered?
-Will it start to become fuel critical, supposed they went to the base?
-If they went to the planned destination, will they consider burning off fuel before landing?
I'd say the deal about making a good LOFT scenario is to not overdo it in any end: nothing should be unrealistically difficult. Often, what makes the LOFT challenging is the very fact that you have many options. If it's all written in stone (everywhere else is 0-0 and the only approach you have is the NDB, the radar just magically went out and the wx is right at minimums), you are not testing decision-making skills, because when there are no options, the decision is already given. The more elements you can put into it to consider, the better. That's my personal opinion, anyway, as a non-trainer, but rather one on the recieving end.