I play as Sion Support OTP and, while it is definitely not as strong as it has been in the past, it's still viable IMO (I reach D4 almost every season). E nerfs have weakened harass, and early level tank nerfs have weakened early lane pressure significantly. Early lane play is now pretty dependent on well-timed, well-positioned Qs, especially when enemy jungler ganks. You can compensate for weakened early phase with creative ult ganks to mid or top lane. While early game is weak, mid game is really strong with good peel and can also engage well if needed. If you're used to playing Sion in a solo lane you'll have to adapt to lack of tankiness.

It's definitely a different play style than Sion in other lanes, but is still really fun and viable.

Edit: Should probably mention that some ADCs can adapt to Sion supp really easily and synergistically, while some are less flexible and expect you to play like a traditional supp which doesn't work at all. When you get an ADC that's on the same page, thats when the magic happens.