What functionality is missing?

Currently, there is no method to import and revise presently made stat block templates. (Or at least not that I've been able to discover).

What is unsatisfying with the current situation?

For someone who makes a whole lot of homebrew rule changes, one of them being the incorperation of higher tiered spell levels, I'd love a way to take the current Spell statblock and change the slider from 0 - 9 to 0 - 15 for example.   Even if by incorporating this tool it doesn't allow a publication/sharing to other DMs, it would still be incredibly useful for those campaigns that, like my own, have minor changes to normal 5e Rules.  

How does this feature request address the current situation?

By giving the option to import current templates and edit them not only can they be optimised but can be personalised for each user of World Anvil, so they don't have to go through the effort of building a new template from scratch.  

What are other uses for this feature request?

Being able to edit and revise currently made templates could help minor changes, like the spell level option I mentioned earlier, but also give World Anvil users a library of previously made assets that they can import with a click to make entirely new templates.   For example, I'd love to have a Spell List template, but the majority of DMs don't create entirely new Spell Lists. By having access to certain HTML features (for example, being able to have a modular table) I'd be able to add a table for each spell level, and continuously add spells to each level. (To create a spell book of my own!)   I'm not a skilled website developer, nor technically minded when it comes to CSS. Being able to copy and paste premade designs and features would help massively.