I'd like them to add the sims 2 romance interactions and some new ones.
I'm not sure if this has already been mentioned in this post but I would love for them to introduce one sided relationships. One sim could consider them their best friend or soul mate etc whilst the other could be like meh I don't like you leave me alone haha. It could bring in new traits like clingy for adults around their friends and lovers which could have a negative impact on their relationship unless the other sim is also clingy.
They make the 'its complicated' relationship more in-depth. There could be an uncomfortable around annoying friend moodlet. They have a good relationship with them but prefer it in small doses. This could work by having complete opposite traits eg whoever has childshish or goofball is the one who might annoy the other unless they have similar traits.
Maybe this isn't all for a dating pack but cute little things like this could really improve the game.