Air defence is not the only job FFGs need to perform, and with the number and quality of AAW DDGs and FFGs the PLAN is getting, I think they have anti-air pretty thoroughly covered without needing to rework the 054s.
Even as they are, they are still very capable FFGs and compares favourably to most FFGs in active service around the world.
For now and probably the short to medium future, I see the 054s as having a great potential role as dedicated training ships to help train up the large number of new crews the PLAN would need for their rapid growing fleet of 054As.
Even after 054A production stops, they could still serve in a training role as with the size of the PLAN 054A fleet, replacement crews are likely to be needed fairly regularly.
In a combat scenario, the 054s would make great ASW FFGs, freeing up 054As to focus on AAW.
The 054s are very new and capable FFGs, and there is zero need or justification for getting rid of them anytime soon, especially since the PLAN still have so many JiangWeis, JiangHus and 051s that could do with replacing way before its the turn of the 054s.