Combining Tornado and Flask templates
You are not bound to the default template engine in Flask. Maybe you could somehow use Tornado's template engine in Flask, then it'd be possible to use the templates in both.
Is possible to combine Tornado and Flask web templates together? 
For example: Use Index.html as "base" template setting up block for extensions:
Then ,extend index with "block" from Flask for Flask Routes
Then, extend index with "block" from Tornado for Tornado Routes..