I wasn't gonna share this until I finalized the design, but something I've been toying with was a system for 3 spells, and melee weapon skills changing how spells behave.
The former would sort of simulate what we currently have. I call it The Rule of Three, where you'd have to juggle casting Verfire, Verblizzard (new spell), and Verthunder to generate Mana (unified as one bar instead of White and Black). The idea is that you'd still have to cycle through Verfire/blizzard/thunder when at range (like running away from a mob's telegraph, or the mob opening distance between you and itself), while being discouraged from using the same spell over and over. Now you'd say "but then you have 3 spells that do the same thing instead of 4", but that sort of ties to the latter system.
The latter would be working spells into combos by having melee weapon skills alter the effects of spells. For example, Verfire would have a range of 20y when hardcast (2s cast time) and deal 180 potency in fire damage. But when used after a weapon skill, Verfire becomes a spell that casts instantly, has a 5y range and deals fire damage with a potency of 220. Verthunder would be a 20y range spell that deals 180 potency thunder damage when hardcast, but if used after a weapon skill becomes an instant-cast DoT with 24s duration.
The catch between both systems is that spells comboed with melee generate low/little mana, but your DPS tanks if you're just casting spells from range. This ties into two other tentative abilities:
Spellblade - Requires at least 30 Mana. Empowers your weaponskills, increasing their damage. Effect ends upon reuse, mana levels dipping below 25 Mana, or upon executing Redoublement. Cooldown: 2.5s.
Chainspell - Requires at least 50 Mana. Removes the cast time of spells used. Duration: 1s per 10 Mana (maximum of 10s at 100 Mana).
The idea there being that you're choosing how to spend your Mana depending on where you are. If you're at range and won'd be able to close the gap anytime soon due to mechanics or forced distance, you'll want to pool Mana for Chainspell. If you will be reliably in melee-range, you'll instead toggle Spellblade on to empower your melee combo. The idea still needs work, but that's what I got so far.
All this being said, the system currently in place can work, but needs notable adjustments to make melee an integral part of gameplay.