@Devs:
It would be great if you provided the next row to go to after entering pattern data. Making your own routine like that is quite tedious if you want it to be fast and 100% compatible, as it needs to handle editsteps that skips patterns for example (when in continuous pattern mode).
Suggestion:
renoise.song().transport.next_seq
renoise.song().transport.next_line
This tool is buggy and not compatible with the native behaviour. (Add two patterns with only 4 rows, set the editskip to 32 and you’ll get what I mean.)
A fully compatible and fast script is rather big for this simple function, why it would be nice if the API provided it. The data is already there, somewhere in Renoise 
Possibly, but it is already hard to get the exact current position on-par. We need this as well before we can use things like your suggestion.
Or did you had something in mind like?:
renoise.song().transport.next_seq = renoise.song().transport.next_seq + 1
renoise.song().transport.next_line = [b] renoise.song().transport.next_line + 16
[/b]
No, no. It is read-only, and only provides the same sequence/line number that you would be on after editing in the pattern.
It won’t have to be more real-time than renoise.song().selected_line_index is today.
But this kind of info you already have? I think creating a good class script that does this calculation (incorporating edit step, current pattern size, current and next sequence position) should resolve this as well.
I assumed you wanted something for realtime calculations during play.
What I said before. A 100% compatible function is not very fast and small. Since it’s a very basic function that already is available someplace in Renoise, it would be nice if the API provided it.
(Meanwhile i am doing a recursive function that goes one step at a time until i = editstep.)