I find it baffling that some people are so attached to weapons that are designed as long term projects, and while SE has made attempts to keep said weapons relevant, there will come a time where they will have to be phased out for better equipment. That's how progression works, and regardless of the millions of gil or hours spent putting it together it's for the good of the game to reset the playing field and allow people to aim for something new.
That being said, Matsui's proposed idea leaves a couple of questions. Firstly, whether the first step into Adoulin content will entirely be balanced around 99RMEC weapons.
Secondly, if in accordance to these weapons no longer being the best, will acquisition of the components see improvements and/or the amount of items/kills required to upgrade RMEC weapons be adjusted.
In some cases the WS are nothing special, while in others said WS have been on/off switches for viability (PLD with Atonement, DRG with Drakesbane, RDM with Chant du Signe), so being able to unlock them for general use would be a wash, IMO.