I would say ultra-wides are a good alternative to a multi-monitor setup; But not necessarily good in a multi-monitor setup.
If you're just looking for screen real estate and don't much mind about PPI then there's a bunch of new-ish ~32 inch FHD high refresh rate monitors out. Especially with a wide curve and small bezels I think these would make a great setup. There are also new (or soon to be released) QHD panels at the same size if you need a slightly higher PPI.
It would be useful if you used some tools like a
PPI calculator and/or
Is This Retina to quantify what you're really looking for in terms of PPI, screen size(s), and viewing distance.
Edit: Usage and budget?