Don't think it has not been attempted over the years. The dynamiting changed the structure such that there is a blowing flow emerging from a small slit. Attempts to dig out the entrance are typically met with the flow filling it back in. The only way this will ever be accomplished will be with a full fledged dredging operation to suck it clean faster than the flow can react to defeat the effort. I have seen some huge piles of gravel and large rocks removed over the course of days, and then looked at the results to see no change in the opening.
It would be nice to see it opened up once again, but I seriously doubt it will ever happen. Morrison was a beautiful cave before the sheriff dynamited it closed to "stop that cave from killing any more cave divers". It is quite deep, which is what generated most of the deaths (diving a cave beyond 200ft on air is not safe, but it is how things were being done back then.)