I really think the accum penalty as a stand-in for a more direct performance degradation as a real stacking penalty is causing more issues than the one it solves.
As many have said and pointed out: anything that also depends on accum is now adversely affected. Shields, ecm, enwar, reps, etc.
Also, the fact that now cycle times being reduced to make fits stable or using lower-tier equipment is totally backwards. Why would T4 modules, that cost more to make, but have less utility for the end-user and therefore less value to them because of faster cycle times? Or why would having high skills with cycle time reduction, even with maxed out accum skills still result in accum instability? More skills should improve performance. If you can't run miners continuously, ore/hr is reduced, and this is the performance metric miners care about.
As a miner/harvester, one should purchase and add more modules to a fit, therefore costing more(value), to increase this overall performance. If adding more performance-enhancing modules suddenly starts making the fit less performative than a fit with empty slots(cheaper; but more effective?): why? why not just reduce the increase in performance per module? So the 4th or 5th module might be a drop in the bucket, but it doesn't go from viable to broken! Now, cheaper fits get more done. Whereas investing more here breaks the fit.
Same for any PVE activity. Now with less dps tunings, or accum instability, less bots are killed(PVP: therefore demand for bots/mods drops*), less materials are yielded, and pve-combat progress slows.
*This is a higher level issue about the life-span of a bot on field in pvp and pve and how that affects market/material demands. I'd argue this demand needs to increase, not decrease. More bots dying faster=good for the economy.
The tuning buffs and penalties on armor rep tunings and indy tunings are having some exploitable 'features'. Very fast harvest mission running, nora explosion on yields, and more to find out!
So overall:
PVE combat is slower; due to lower damage output
Harvesting/mining have potentially high yield/short burst potentials; cause assignment times to drop. token market inflation?
PVP: longer time on field, due to less overall dps. (Stalemates more likely; less death; less material demand)
PVP: more diverse fitting. +1