I've been dealing with serverless since 2018 and have a company with a 100% serverless and open-source product (webiny.com). I'm not sure I fully agree with your 4 issues and the fact that Web Assembly is the answer.
"Serverless functions are slow" -> not really, only if designed poorly
"DX serverless functions is sub-par" -> where's your proof, again you'll have bad experience as a developer only if you don't know what you're doing. Which I see mainly from people trying to approach building serverless applications by having a container-like mindset and that leads them to bad design choices.
"Serverless functions come with vendor lock in" -> I think most of us are beyond the point of that vendor locking is bad choice. Worse choice is picking a sub-optimal technology with lower performance, higher cost and lesser reliability.
"Cost eventually gets in the way" -> Again, only if you don't know what you're doing and make bad design choices.
When it comes to Web Assembly, I don't see how this is a better choice of technology vs something like Node. In node I have a much wider support of the technology than WA (talk about vendor-locking), I have a proven eco system of libraries, knowledge and a much bigger talent pool to source from. The cold start issue you mentioned on your website, I can tell you first hand, the cold start is not really that big of a problem, not big enough that you would want to switch to a different technology and there are many ways to mitigate the cold start problem.
Just saying, I'm far from convinced that there is a benefit in switching. I would love to see more detailed benchmarks and examples I would be able to replicate than just statements in a blog post.