Multi-level ajax select for taxonomy terms

Hello!

We have created a custom autocomplete field widget for large amount of taxonomy terms (30k) which replicates the UI of shs widget. The only difference is rather than loading all the options at once, we are loading the children on parent select to speed up the loading of the taxonomy tree and to avoid the issue with server connection timeout. The autocomplete value were being pre-populated by selecting on the last select element using the ajax command callback. We've had a plan to create a patch for shs similar issue, but we don't think it's a solution since the shs uses OptionsSelectWidget and it might be required to create a separate widget to fix the issue.

Anyone have alternative solution or inputs? Thank you!