I think we should just raise the baseline to ~75/20% and allow 5 stacks (so it'd cap at 100/25%). This would mean it'd be worthwhile all the way rather than just after 4-5 stacks. Nothing else would need to be changed tho the map would need an additional item for AD casters. But I think Sanguine Blade is poorly suited for that anyways since AD casters are all about the burst and SB will always offer the worst damage in the start of the fight. Just a simple 3k "100 AD, flat" item would really help.

One way to change Sanguine viably would also be to make it start at full stacks and make it deal reduced damage with each additional attack, to a minimum of ~60/15%. It wants blood, not dragged out fights. This'd make it work when it's at its most important (in the start of each fight when carries do their primary, lethal burst and when AD casters use their abilities) and then be balanced by being weaker in longer fights. I think I'd prefer this to all the other solutions, to be honest.

Sanguine Blade isn't meant for AD casters or tanky dps. AD casters already have plenty of high AD burst options out there, and tanky DPS have plenty of sustain and their damage doesn't need any buffs.

Riot doesn't want any champion can benefit from stacking damage to have nigh-infinite sustain. This should have already been apparent by the global -20% healing effects debuff.

By allowing a high-damage high-lifesteal item Riot would guarantee its purchase on EVERY champion that auto attacks or scales off AD. With the way it is now, Sanguine Blade is only really useful on ranged AD carries and Master Yi.

"- Does not stack on Abilities."

It sure as hell stacks with Ez's Q.

It's basically meant for carries, and only carries. If it gained stacks from abilities it'd be better than Entropy, which is the new 'raw damage' item for everyone else. It's fine as is really, but a 1 second increase on the stack timeout wouldn't hurt.

Allow it to stack when your casts deal dmg, increase stack duration by 1-2s. Nothing else.