The gear is still ingame. So take a look at the stats and compare and judge for yourself what the implications of adding not only con, but also critigation, tenacity, AA, protection, dps, hit rating, crit rating and crit damage rating to the equation.
With khitai the crafted blue gear (which by the way you could trade or buy, the grind involved only getting money or getting friends) this shifted a lot and the gap between new 80s and others became larger.
I was totally new back then...and even me could hurt the top noth players back then on 1 vs 1. Try that now without exploiting. And when you got "oneshotted", it was a clear bug or exploit...not like now, when it has become a standard game mechanic. Taking down a raidgeared char took longer, you were not allowed for mistakes, but it was possible with specialization and focus, because not all stats were exponentially higher (only some). You were not a fly to be ignored, if they did this, even the new players could get dangerous. Again...compare now. This is what i meant partly by being caught in the d&d power loop (happens when gms give out too much power and too fast...players will become dependant on the gear and demand more and more).
Where is the drawback (except work, but this varies a lot on how you do it) in seperating pve progression from pvp progression???
You could have basic stats working everywhere, PvP stats and PvE epic stats working only in PvE. You also could add gear enchantment modifiers to zones (this would even be within the lore...places of power or dead magic zones), thus controlling the gear effect...and even create interesting variations on mini games or open world zones. As well as giving the devs an additional tool for pve difficulty they can use.
Especially when you create new gear anyway...the work amount of adding "epic only" stats should not be too high, because you avoid relaunching the whole database.
On a positive note, just from reading the letter, i see no clear statement, that they do not intend to seperate the progression or that they intend to repeat past mistakes.