Hmm, though I'm not a programmer, wouldn't it be possible to simply add a text field for each cell in the admin section that places any code string within the td tag referenced? It could be like the existing "Custom Data Field" input, only it allows for any code string to be entered for the cell td tag in question.
Otherwise, it could just be a small number field that is hardcoded to colspan only so that I only type in a number to represent the cols spanned. A second field could be hardcoded to rowspan too.
This way I could put anything like
colspan="4" (or just "4" in the hardcoding case) in the first cell and that would be added as an attribute to the frontend code within the td tag for that cell.
Incidentally, this would be flexible and allow me to add a colspan attribute to any cell for just spanning 2 cells from cell 1 to 2, but not 3 and 4. Or, spanning 3 cells from 2 to 4 or whatever since each field would have its own colspan (or rowspan) designation.
Of course, any remaining td cell output would have to be omitted from the frontend. In other words, if I spanned 4 cols on the first cell, the plugin would have to be smart enough to not add 3 more empty td tags for that row.
And, ideally, it would be reflected in the admin data entry section too so that either the entry fields are combined into one field (in the case of spanning 4 cols) or at least the remaining fields are disabled. Of course, the admin fields could simply remain as is and the user must be mindful of their own colspan code and not add any data to remaining cell fields for the row.
Yup, these projects always get complicated! Anyhow, thanks for listening.