First, let's come up with two stances. The first we'll call "Magic Fencer" and we'll loosely call this the Enhancing side. The second we'll call "Runic Knight" and let it emphasize offensive casting. Now, while either of these are active, Enspell damage inflicted will build toward a pool, a bit of a mix between Sublimation and DNC steps. For every 30 Enspell damage inflicted, you will gain 1 level in this pool, up to 3, that you can then apply to a spell via another set of abilities. We'll simply call them "Feedback I, II, and III" for sake of demonstration.
Code:
Magic Fencer effects with Feedback:
Feedback I II III
Duration: +30% +65% +100%
Phalanx: +2 +4 +6
Haste: +3% +4% +5%
Stoneskin: +15 +30 +45
Regen: +3 +4 +5
Refresh: +1 +2 +3
Blink: +1 +2 +3
Aquaveil: +5% +10% +15%
Barspell: +10 +20 +30
Spikes: +1 +2 +3
Runic Knight effects with Feedback:
Feedback I II III
Duration: +30% +65% +100%
MACC: +5 +10 +15
MATK: +5 +10 +15
CMP: +10 +20 +30
Slow: +3% +4% +5%
Paralyze: +1 +2 +3
Blind: +5% +10% +15%
Poison: +2 +4 +6
Bio ATK: +3% +4% +5%
Dia DEF: +3% +4% +5%
Prior to using any of these boosts, you'd have to pop the appropriate tier of Feedback before casting. It would only work for that spell and then deduct the appropriate amount from your Feedback pool. Feedback I would be first gained at 55, II at 65, III at 75.
For those interested in playing RDM as a tank or a more rounded party buffer (Especially with Accession), they'll probably flock to Magic Fencer. I'm on the fence with this stacking with Composure to allow like 12 minute Hastes and such on the RDM, but the main goal is to reduce your cast load on other people and therefore giving you more time to swing. These also technically eliminate the need for Haste II and Refresh II as spells, or at least allow the former to go to WHMs. Spikes enhancements are a bit more general, but figure Blaze to do more damage while Para and Stun proc more on the others.
Runic Knight should obviously portray itself as the offensive aspect. All enfeeble durations would be upped, making a RDM/BLM ES+Slow II comparable to a BRD's ES/Troub Elegy in duration. Paralyze would gain a minimum number of procs, Blind reduces ACC more, Poison gets more DoT, Bio/Dia's respective status downs also get a boost. The MATK is there if you want to partake in MBs. The presence of Conserve MP is to promote uptime since the costs of T2 debuffs and T3 nukes is rather high.
At present, a RDM with Enhancing Sword, Fencer's Ring latent active, Lycopodium Earring, Hollow Earring, and 300+ Enhancing Skill would get around +33 per strike on T1s if the mob isn't resistant or has Shell/MDB. Technically, a lot of RDMs would probably just use Joyeuse (and off-hand Justice) with Fencer's and settle for +25. This should allow time between recasts to build your pool up for another Feedback if you're going to be using exclusively on one spell. To some degree, it'd also allow hopping between modes if, say, starting a fight in Knight and switching to Fencer after landing your debuffs. Pools would also reset when switching, too.