To whom? I see many people who need a trivial amount of server logic. Right now, they can do one of 3 things:

- Use a random site who may or may not radically change their business model in the new few years. - Pay $5/month for a VPS, then get forcibly dragged up the learning curve of becoming a full-time sysadmin - Pay pennies for Lambda

Is there a reason to re-write your backend? No. Is there a reason to consider it on your next project? Possibly.

Since any site "may or may not radially change their business model" at any time, you really only list two substantive options:

(1) Use an VPS, or (2) Use Lambda

But, really, there's a more choices:

(1) Use a VPS or IaaS (with full sysadmin overhead), (2) Use a PaaS (like Google AppEngine) and avoid sysadmin overhead (but probably have more code than a "serverless" function host like Lambda), or (3) Use a "serverless" function host like Lambda

You probably don't want to do #1, since for low-volume and trivial logic its (1) comparatively expensive, and (2) high sysadmin and programming overhead compared to the other options.

#2 is lower overhead (particular on the sysadmin side), but still more than #3. But possibly cheaper (e.g., if the requirements fit within the free quotas for AppEngine.)

#3 may be the best solution for some things, but its not as stark as a choice as you present it to be.