No, I don't have any experience with folks moving to, or from, TaxCloud.
We do have some folks using this plugin because they only have nexus (locations) in WA. Of course, there's a possibility down the road that merchants would need to collect taxes for shipments into other states and that would require something more robust.
We have also developed another plugin for Avalara's Tax service (a competitor to TaxCloud, in a way) and we've helped customers get setup with it. It's not yet available through our site, but if you've got a customer interested in Avalara's service let us know or check them out at:
We may look at TaxCloud in the future, but there's already a TaxCloud plugin for Shopp and that's our main e-commerce platform.
Right now, I can't see any problem with a WA merchant starting out using this plugin to get destination-based taxes and, if they expand into other states, or laws change, they can graduate to Avalara or TaxCloud. Of course, she could also start with growth in mind and signup for Avalara or TaxCloud from the start.
Personally, I'd probably make the call based on the size of business and amount of commerce. If they're a million dollar company, Avalara's tax calculation, collection and submission service may make perfect sense. On the other hand, if she's just getting started and has no idea what her sales will be, I'd start with this plugin.
The switch won't be hard later; it'll just be a different method of calculating taxes and will require some settings if she's using TaxCloud or Avalara.
Let us know if you have questions.