Not sure if its been covered but given the extreme depths that are likely involved the dye suggested may never actually make to the surface let alone anywhere near the prang.
There are thermal layers that affect acoustics I believe, so a dye solution may never appear .OK at shallows probably but them you would likely find the recorders anyway.It would certainly be helpful in many cases.
Anyone seen smoke from a large fire on a very calm day , sometimes the smoke appears to hit a glass ceiling and commence to spread out?
Given many airliners now use solid state recorders ie the fairchild 2100- series that are much lighter than the old models how about just adding to battery capacity ? All solutions will cost but suspect adding capacity in future maybe a relatively cheap option.
Live info squirts via satellite / acars for example maybe ok if they are only triggered by an event , ie engine out , manual ops by crew, excessive rate of descent, excessive g forces, loss of cab pressure etc.
Otherwise just too much info & too many flights to record.Much less to record / monitor if only triggered by an event.
Just brainstorming..