Have any solo travelers booked a shared water taxi/shuttle from the airport to Venice?

These are third party vendors. They could accept your reservation and cancel the night before if they have not found anyone to accept your business. Perhaps ask your landlord this question. They may have a "cousin" who could help you out.
Perhaps, join Venice specific Facebook groups. You could post your question there, where you'll find real-time, on the ground info.
Good luck, and enjoy Venice!

I'd just take the Alilaguna, they work just fine.

The regular land bus (or taxi) to P. Roma and the vaporetto from there works very well also. Not only is it much cheaper, there isn't any need to set up anything ahead of time.

Nothings tops a private water taxi for arriving in Venice for the first time. So splurge if you’d like!

But otherwise I agree with TC’s advice, and that’s exactly how I managed my arrival last week.

We have used the shared water taxi, without reserving in advance, three or four times. While they appreciate reservations, they aren’t necessary, and we hesitate to reserve if our flights might be delayed. We’ve waited 10-15 minutes at the most for five or six more people (solo travelers included) and we walk as a group to the docks. Their desk is in the airport’s main arrival hall, toward the end near car rentals. It truly is such a great way to arrive with the additional advantage of not having to deal with bags on the Alilaguna. They also have a desk or kiosk at the train station, I believe. Have a wonderful trip!

The bus is quite easy as well. Drops you right near the train station.