Great to hear from one of the developers in the forum... congratulations on what you guys have achieved thus far and big hopes for the future especially with a much needed HTML component which will take Wix into a whole new league.
Thanks to Adva for pointing out this post which i would have missed if it weren't for her heads up on it in another thread.
I can think of trillions of uses for the HTML component but ones which immediately come to mind for me specifically mentioning the services so you can check out their embed code are as follows:-
a) for it to support simple iframe capability which would thereby allow the wix site to be the primary customer facing site and allow us to integrate functionality in a very cosmetic way for content, web pages and services which are not available in wix currently. Full iframe support for large frames would be a must and the ability to show or suppress scrolling bars on the frame.
b) embedding of the swf object in a html component is a strong contender as it will allow more sophisticated swf (and flash objects) to be embedded, specifically ones which use xml files and skins which can't be currently implemented because of crossdomain issues or external xml files. This would also get you over the hurdle of enabling ActionScript 2 swfs as it would delegate this handling to the swf object in your html sandbox.
c) embedding of wufoo forms and polldaddy.com polls and surveys
d) embedding of database functionality from third party companies like dabbledb.com or zoho.com would fill the hole in the current lack of a database ability.
e) embedding of a video chat service like tinychat.com or userplane.com
f) embedding of broadcast video from sites like justintv.com, zaplive.tv or payperlive.com
g) embedding of the other video hosters like vimeo.com, viddler.com, bliptv.com, stupeflix.com, screencast.com and animoto.com
h) embedding of viral marketing content channels like Kyte.com, sproutbuilder.com, toufee.com
i) support for popular widget libraries like widgetbox.com and Universal widgets from eco.netvibes.com
j) integration to customisable social network services like SocialGo.com or Webjam.com which would allow membership management, blogging, forums and event management - iframes here would do the trick.
k) document integration services like issuu.com and docstoc.com. Issuu is a great service where pdf documents are uploaded and then made available as online flip books for embedding in html containers.
l) file storage and sharing service integration for sites like box.net, mediafire.com etc.
ok, that's enough i think and should give a nice cross sample of code requirements from embedded objects, javascript and iframes

If you want more i can happily give you some more references of neat services for integration.
A suggestion i have for a nice feature would be to do what netvibes.com does on it's html components on it's start pages... that is to only process and render the html when the html container is set as open. This allows many html components to be inserted on a page but only the ones set as open by a user click on a header button, are visible or not. This could be a very nice optional paramater for each html container and allows for a tidier page layout but dynamic in user interaction. It would also improve the loading and rendering of a page as only the open containers need to be fetched and rendered.
My 10 cents

and can't wait to see what you come up with. If you want any help alpha testing i would be happy to help.