So my concern is the upwell hauler simply make the old haulers feel like dated content to the point as being seen as irrelevant sure the tech 2 version has its use but comparing a tech 1 upwell hauler to a tech 1 empire hauler why on earth would you ever want one.
So the suggestion i have to make the haulers still be relevant is a slight increase to there base EHP while compensating this with cost of manufacturing the haulers each empire now only has 2 haulers one for speed while the other for more cargo.
Also due to the removal of the other more specialised haulers for some empire factions new rigs will be introduced to change cargo yet only allow you to store one type of cargo in that hold selection. For example you put a ore cargo rig in your hauler and 33.3% of its cargo storage will be converted into a ore hold with the ore hold would have 33.3% of that cargo + additional space due to the specialised nature of the ore hold.
That means you can put 3 rigs of say different cargos having 3 different holds or put all 3 of the same rigs turning the ship into a 100% of that hold type.
Think of the rig slots like how a truck in real life changes its carriage.
Now the reason i suggest this for rig slots is because it adds additional choice to your current rig selections as well as not needing to add a completely new ui element to the fitting screen.
There will also be a special warning for these rigs if you have any cargo in your ship it wont allow you to remove/add the rig.