There needs to be a mix of housing, 'hot desking' type office space, covered market/pop up shop or food businesses, leisure, exhibition plus maybe showrooms* and even car parking, because in a lot of cities and towns, a big barrier for people going in is high parking cost, but public transport that is also expensive and infrequent and all this does is drives people to out of town shopping centres, where they can easily park for free and come and go as they please, rather than time visits to coincide with a bus service that is hourly at best.
*Showrooms because some retail doesn't lend well to online only, so it would be useful to be able to go and actually look at physical products, ask questions etc. Some brands might find it worth their while to have a presence in busy locations, especially if people can actually get there easily and cheaply to look at their products, even if they have to order them for them to be delivered to their homes.
Personally, I'm hoping that we'll finally get a Uniqlo in Leeds as surely they'll now want to move into the empty Top Shop, Debenhams, Dorothy Perkins, or one of the many other shops that are now empty.