Thanks! I was actually looking to use Bootstrap 4 for the theme, but it’s still in the Alpha stage and I’m not sure when the official release is going to be, so I might consider using Foundation 6.
Anyway, another thing I forgot to mention is that I always thought for some reason that support was IE9 was mandatory for WordPress theme submissions at Themeforest, but now I’m not able to find it, perhaps I misread it somewhere; however, do you think not having support for IE9 could be an issue for your buyers?