I love the tan interior but I personally wouldn't combo it with hethel. The tan has a lot of yellow in it, yet at the end of the day is brown. To my eye it clashes and doesn't compliment hethel well. Hethel feels like a flashy modern color, whereas tan has a more subdued old -school gentleman-spec vibe and is best paired with neutrals like silver or black, or classic pairings like racing green or red.
I ordered my Emira in nimbus, black pack, tan interior, and yellow calipers. A bit boring, but the colors combo really well and I like the classy vibe. If I did hethel I'd just stick with black interior personally. Which also allows you to get the alcantara option, which given the relatively little bolstering on these seats, helps keep you in place when pushing it on the bendy's.
But at the end of the day, it's your car and your spec, so do it if you dig it!
Figured I'd attached a pic of my spec (that I saved from a post of
Shahaf2911) -- the tan interior is so nice.