Incremental Refresh

schoden 

You are correct with your assessment of incremental refresh.  It's mainly a tool to reduce the 'load' on dataset refreshes by only importing a part of the overall dataset.   

Unfortunately, once you've created an imported model - there is no way to 'convert' it to a direct query model.  You'd have to essentially start over again (and select "direct query") when chosing a data storage mode.  

Yes - direct query moves the processing back to the source database - so there are real concerns about performance and datasource stressing - depending on how many users and queries are being applied simultaneously.  However, this method will allow you to get 'near-real-time' info - each time a query is run - or a page is refreshed.  (In the service this can be 'forced' with a browser refresh).  

I do not have much experience with pushing datasets with Powershell.  I imagine - if you could programmatically 'force' a new dataset into your model (every few minutes?) - you could also achieve 'near-real-time' results.  This would be similar to simply refreshing and re-publishing your PBIX file at a regular cadence.  There are no limits that I know of - to how often you can manually re-publish a dataset.