It will be great, and i think it's probbably easy to add new feature in Form Sections customization.
The idea is to add a combobox to select "Tabindex Direction" (Vertical/Horizontal). This allows end users to set the tabindex behaviour in the form section.

I have a lot of customers that requires to have tabindex order in a horizontal direction (the default direction in the section is vertical).
I know there is a workaround to do this if I create small sections with just one row each, but i think it will be very usefull (and maybe easy) to add this feature to end user.

Thanks in advance!

Regards