“another possibilty would be, autofetching rows, when scroll down to the end”
that would be the ideal solution. I 'data window' proces/thread as a layer between the GUI and the data base. That is a complete architecture change and will take much more time to prepare.
If you did not notice the 'check all' now (beta3) disables when you are switching tables. But still you may INTENTIONALLY 'show all' and experience that it takes much longer time than you expected. There is no way to stop the loading as of now.