Hi there, I'm Matt Sergej and can implement such site for you (23 years of IT development, web mastering and multimedia work experience, last 5+ years scripting SVG animations/visualizations).
I've checked all your referenced sites, created WordArt for my birthday today (thanks!) and know what needs to be done for such site (emojis are extra, right, next to words that WordArt uses?).
Here are some features to discuss though:
1. The auto save feature and say potential (tens of) thousand users online at the same moment require fast and reliable (web) server solution. What can you use - node.js and "NoSQL" database solution (like node.js Meteor and Mongo) come to mind?
2. Storage and bandwidth are related to the dedicated web hosting (and "secure shell" access) in previous point. These needs to be calculated well before implementation plus be ready for "scaling" (number of users increasing over time).
3. Should the site work on mobile devices, probably at least on tablets (with 1024 pixels or more wide screen)?
4. Shape conversion - this requires quite an algorithm for vectorizing bitmap images (PNG, JPG, GIF) while using SVG is easier. WordArt does use canvas though for displaying wordarts and overall this is complex to implement perfect.
5. Finally you probably expect several different CSS animations to embed (I see just one in WordArt).
Looking forward to your reply. The bid is realistic, I would work every day to develop your site.
Best Regards,
Matt