I would imagine that it is to do with very light loads- I last flew into MCO in mid September and my a/c had less than 60 in Y! With schools not breaking up for another couple of weeks and half term long gone I would imagine this time of year is very quiet on the MCO route. I doubt it is due to a technical issue with an a/c normally VS will fly in another a/c to operate the route.
I wouldnt worry too much about it- if your flight does get cancelled you will either be transfered to the other MCO flight or fly the next day and be payed some kind of compensation. In the past on cancelled VS flights I have heard of free Y round trips being offered.

If your flying over Easter dont worry- you flight will certainly not be cancelled due to light loads and VS would ring/email to inform you if it was.