If I remember well, the only thing that really came out of that was that ricklessabandon did some experimentation on Muramana on the PBE, giving it an active where you spent an increasing amount of mana to deal true damage on the next attack, then pulled the changes.
No matter how one spins it, mana is nothing but a gate to one's kit, existing purely as a restriction to one's casting ability over a long period of time. This, however, could be perfectly fine on its own, because at the end of the day, resources like energy and fury also exist purely as gates. The problem comes from Riot trying to force certain champions to itemize for mana, whereupon a whole bunch of different issues arise: for one, mana itself doesn't feel interesting to buy, because it doesn't actually directly increase one's combat power, only one's ability to cast more spells in the long run before going back to base (and even then, that becomes less relevant as mana pools naturally increase and people die faster, so buying the stat always feels like somewhat of a waste eventually). The bigger issue, though, is that mana itemization causes mana champions dependent on it to become dysfunctional: because they need the mana to operate, they essentially cannot function properly with the resource they are innately given. Mana therefore gets purchased not to truly enhance one's strength, but simply to remove a measure of dysfunctionality in one's kit, which I think is pretty shitty in terms of overall enjoyment. It is therefore no surprise that the stat feels more restrictive than other resources, because it is, and so deliberately for the sake of having a stat on items that shouldn't need to be purchased in the first place.
Because of this, I think the way to go should likely be to remove mana from itemization entirely, and standardize mana pools to 100 at all levels, with appropriately lowered costs and regen amounts for each. A current problem with mana is that it's often difficult to compare mana usage across champions, due to the vast discrepancies in mana pools, regen, costs, and so on (by contrast, energy and fury usage are both very easy to compare across champions with the same resource). Standardizing mana so that we can tell the difference better between champions who cast a lot, but then have a harder cap (i.e. low costs, low regen relative to their mana pool), and champions who run out quicker, but also recover more quickly (i.e. higher costs and regen relative to their mana pool), could add a lot more clarity to mana and how it's intended to gate kits. This would also require some adjustments to certain champion scalings (e.g. Ryze's stats-for-stats innate), as well as mana items (GLP and RoA might need to scale a little differently; Tear and its upgrades may need to disappear completely; supports would need to rely on a stat other than mana regen on their items, etc.), which is a shame considering how the recent AP item changes left mage items in a pretty good spot, but I think it could be much more beneficial to the balancing of mages, and mana users in general, in the long run.
