Feature Request: Pull based virtualized list

[wSedlacek]

Is your feature request related to a problem? Please describe. I am looking to create a infinitely scrolling list that pulls data from an API. It would like to be able to start a request to pull data for what is currently displayed.

Describe the solution you'd like Much like how RxJS is used for pushing data, I would like to use Iterables either with IxJS or a similar data structure so that when an item needs to be displayed .next() is called. For my use cases the .next() call would need to be async, so AsyncIterator might be a good data structure to start with. However it may be nice to provide some pattern that allows batching.

Describe alternatives you've considered I believe the @angular/cdk has a somewhat similar pattern with their DataSource class used for their virtualized scroller and data table. I am not sure that it would need all the requirements to build out the interaction I am looking for, but it would be a good start to getting towards that.

Additional context