Large Dynamis linkshells as they currently exist will no longer work. THey will have to adapt to the new system. That's not impossible to do.

Having a single person pay for a run's hourglass will no longer work, as it will now be a one-time purchase. However, these 'run sponsors' can instead put their gil towards purchasing more currency, as at least some players will be entering dynamis on a daily basis to farm currency for profit. (Chances are RMTs will try to do this, so keep an eye out for them to report them to the GMs.)

This is not the end of Dynamis. As it is, even 12 players of level 90 can clean out a zone with the right mix of jobs; and it is reasonable, I feel, to assume that the new Key Item system for NM pops will make zone bosses (including the Dynamis Lord) feasible to take on.

The questions I have are if it will be possible for an alliance to take out the dynamis weapons quickly enough, and if Yin and Yang will still need to be slain simultaneously or not.