I am not sure if it's helpful, but I did an U50 analysis on a casting warlock and here it is:
U50 Preview 2: Endgame Itemization Adjustments (ddo.com)
Overall, I think you can expect to completely re-gear as the stat squish isn't applied equally. For example, legendary crown of snow and attunement gaze both provide +7 spell focus and +4 insightful spell focus today. As of U50 legendary crown of snow will provide +4 / +2 and attunement gaze will provide +5/+3 because it benefits from raid scaling. It's the only +5/+3 item I could find so suddenly it's best in class for generic focus mastery, but there are individual items with+6/+4 for specific schools such as the magewright set (illusion and enchantment only).
Flamecleansed fury set gets a proxy buff as it now has the same stat/dc bonuses as esoteric and magewright. That + clouded dreams looks really tight.
a 2-piece legendary greensteel set goes from 18%hp bonus to 7% so it was hit harder than most items, presumably because the dev that made those items is gone and the devs are maybe sick of hearing how good lgs is.
Mysterious cloak level 21 version remains the same and has better stats than equivalent legendary items. Thunderforged all of a sudden deserves consideration for an off-hand caster item if you don't use LGS. The combination of legendary might of the absishai + legendary elders knowledge + clouded dreams with a gem of many facets with the right set bonuses on it looks really good for a caster. You only need one legendary elders knowledge item if you have the gem with both set bonuses (but of course its random with MANY possibilities).
So stock up on your jeweler's toolkit now!
As far as U51 DC casting will be much easier - it's effectively going away as a speciality - you get max dc by going tier 5 in any epic destiny in a caster or hybrid tree(such as shiradi). So a favored soul could go wisdom-based horizon walker bow in shiradi for dps along with top-tier dc casting instead of relying on spellcasting for dps. You won't match the favored enemy damage of a ranger, but it will be far better than spellcasting dps and you can still have a workable soundburst/implosion/greater color spray/comet fall for aoe crowd control. Gearing would be wallwatch + magewright for starters.