Hi Gavin!
That is important topic and we are glad you mentioned it. We do plan to release new versions of X-Cart 4 for at least 5 years as we stated in the blog post in the
Support of X-Cart 4 section.
http://blog.x-cart.com/x-cart-5-beta-testing-announced.html#A5
Also, I would like to point out that X-Cart 5 beta is
downloadable solution, not cloud, so you might want to test it out as well.