Spell Vamp being stronger and more accessible has the potential to create similar problems with AP bruisers - you can already see problems with Vladimir in this department and I expect you'd see similar cases with champions like Swain, Cass, Ryze and maybe even Elise. The game really doesn't need more champions with the ability to turn into raid bosses as the game progresses.
Ryze? Elise? Come on
Spell Vamp is not much of a problem as you may it look like
Ryze problem wasn't with Spell Vamp and will not be Spell Vamp. Ryze problem is: should a champ be able to spam relentlessly skill chained one-next to other while remaining healthy for the game? The problem on old Ryze was that it was all a matter of range, if he had too much range he would wreck anybody, otheriwse he was useless. Add this to his very efficient offensively and defensively itemization based on mana, and you got possibly a monster which dealt tons of damage while being unkillable, and Spell Vamp (both ulti spell Vamp and eventually acquired with items spell vamp) was only the cream on the top of what was the deeper problem. Deeper problem that has been probably mainly solved thorugh Ryze rework that at least mitigate the problem by limiting the moments where Ryze can keep spamming spells, and new Ryze revolves about this management, again Spell Vamp becomes just the cream on top of a Ryze playerthat is wrecking enemies by his onw ability
Elise has literaly one spell on which she can apply full Spell Vamp and is somewhat spammable (not even that much in reality), and is not even that spammabale as the short range put her anyway in danger so have sustain rather than damage become an extra strategic choice, not an overbearing thing
On Swain, Vladimir can Spell Vamp represent a problem? Yes, but it makes them basically invincible in what were yet match-ups really favourable to them (or the ability of the player make them favourable), as they are limited by range first and foremost. While it IS true that LOL, unlike DoTA, does not aim to balance champions by making all of them unbeatable in certain situations, and Spell Vamp could make Swain, Vlad that some times, it is also true that it is actually possible to play around their kits with enough champs that honestly it becomes more a problem of tweak some numbers and skill mechanic (hey, I'm looking at you Vlad Q CD at later levels) than throw in the bin Spell Vamp completely
Cass... well, is the same question as Ryze old and new kit, and it relies more on actually resetting CDs and earning power and dealing damage through hitting Twin Fang and the numbers of her kit rather then being a problem of Spell Vamp that is eventually just the cream on the top of the cake which represent eventually the core problem (just as Vlad and Swain)
The claim on Spell Vamp helping burst mages and assassins is kinda skewed, too. The problem of burst mages and assassins remains the one to find balance between their abilities to kill the target and the possibility of the target to reply or not allow burst mages/assassin to dish that damage without being in huge danger to die. Use Akali as example does not work because Akali had different problems, the spammable skills and being manaless with low CD and being capable to regenerate easily energy while being capable to going in stealth mode baing non hittable and receive armor/MR on the old twilight shroud if you could spot here + a respectable ulti range before the nerfs, and Spell Vamp only worsened the situation without being the true roots of them...and as a matter of fact when Akali was hit by those other nerfs, people have not had a legit reason to complain about her unkillabilty since then even though the Spell Vamp is the same and potential damage outcome - and thus healing given by Spell Vamp - has ever increased IF she can get in range, which is much more dangerous and difficult
It is true that Spell Vamp could/should be changed, but not because it is really unhealthy to the game right now in terms of overall balance, but because it does not actually represent a strategic choice if build Spell Vamp or not...it is just a stat you build on few champs because they need it desperately and you pretty kind ignore on everyone else, while it should really be a strategic item build path that give an alternative to the actual ones available for AP champs, as partly happen on lifesteal that represent a secondary but still relevant factor in picking AD champs build and certain items over other