re: Should recruits be able to sign a LOI @ any time?

No. The points from the school perspective have already been made, so I won't revisit them.

From the player's perspective, it's ultimately their choice on where they want to go to school. A lot can happen between a summer recruiting trip and February.
Family situation can change, i.e. a parental job transfer.
Could make new friends at an all-star game.
Break-up with a girlfriend.
The Coach who recruited you could either be fired or moved on to another job.

Just a few things I could think of off the top of my head. Point being, it'd be grossly unfair to the student to be locked down at one school as early as July or August of his senior year.