e-commerce in Tornado (non-blocking) VS Flask (WSGI)
Not an answer but as an alternative way django with satchmo is very suitable for that sort of projects.
There are two flask estensions you might leverage:
https://github.com/MediaSapiens/flamaster and
https://bitbucket.org/lost_theory/flask-stripe-blueprint/
I hope it helps.
Finding a really good python-based e-commerce solution is still hard.
Some things to look at
Satchless http://satchless.com This is a flask-compatible framework agnostic shopping cart solution.
Saleor http://getsaleor.com (django not flask or tornado)
Saleor which is django-based seems more mature and currently maintained. Last update was 19 days ago on github. I would look into this.
The same developers of Saleor also created django-payments.