The shortcode roadmap has a second draft ready, and it's a big improvement over the first draft (better off to read the extended discussion on that if you need to catch up). It's obvious a ton of thought has gone into this, and the new roadmap has changes proposed from WordPress 4.4 through WordPress 4.7.
The change in 4.4 is a new delimiter to get around using HTML in shortcode attributes. Robert Chapin uses the following example to highlight the old versus new syntax:
Old: [form-plugin][form-field1 start="<html>"][/form-plugin]
That is the most immediate change. You'll also notice that compared to the previous proposal, the base syntax for shortcodes is unchanged; the changes are for including HTML with a colon delimeter on a shortcode, rather than a shortcode attribute.
WordPress 4.5 will require adjusting priorities on content filters, such as those for creating curly quotes automatically and for auto adding paragraph tags. There is also a goal for 4.5 to create conversion functions to utilize the new format, to help get sites off the old method.
WordPress 4.6 would transition away from allowing angle brackets in shortcodes, and would convert them to spaces. The change to spaces was after a lot of discussion on the best way to go about disallowing HTML in shortcode attributes.
And finally, in WordPress 4.7, HTML would no longer be allowed in attributes at any point. Here's an example of what the difference would be from 4.6 to 4.7:
==API 4.6== Input: [shortcode insert="fun"] Output: My fun link is here. Input: [shortcode insert="<a>"] Output: My <a> link is here. Input: [shortcode][shortcode:insert=]<a>[/shortcode] Output: My <a> link is here. ==API 4.7== Input: [shortcode insert="fun"] Output: My fun link is here. Input: [shortcode insert="<a>"] Output: Input: [shortcode][shortcode:insert=]<a>[/shortcode] Output: My <a> link is here.
Altogether, this is a long roadmap and will have its challenges. I highly recommend you check out the full roadmap if this would affect anything about your work, but the above highlights the basics.