If "Ark One" is the baseline, and we have Rorqual and some of the others that are basically different from the baseline in some way other than just visually (we promised that to the backers)
Looking at the reward sidebar and the main-body-image description of Arkitect, I only see visual stuff.
That said, if a stat request is easily granted within the existing xml framework (which covers a lot of stuff) I'm happy to go beyond what was promised.
BUT, we've also had a request from folks to be able to choose the visuals they want and then have a playstyle that they want.
It's very easy to mod ArkOne (or a copy of it) to have different visuals. If desired we can have the end of the Ark dropdown list just be a bunch of "(Visual Only) Rorqual", etc options. There would need to be two entity definitions for each variant (with-stat-changes and without) but that's not a problem.
Or one of the more complex ones like Turtle, and it basically kills the engines of whatever Ark they choose, etc.
Turtle would actually use a different entity type, probably, so that the Ark behavior is handled entirely in xml and there's no special-case C# code for "this unit's engines are not only dead, they cannot be repaired" (those kinds of exceptions pile up leaning-tower-of-pisa style). If someone wanted a Turtle with a different Ark's visuals it's a 5-minute copy-and-paste in the xml.
By having two sets of dials there, the underlying personality of each Ark is maintained, but players are able to have a further level of customization via this economic preferences thing. Which sounds like it goes well beyond the economy, frankly.
Bear in mind that stuff like Turtle or Shadow may not go into the base game because it may not be feasible to balance them or keep them balanced. Making variants is easy, keeping all variants equally playable ranges from hard to impossible
As it is, the economic variants would probably disable achievements (the straight-bonus ones certainly would) by way of indicating that it's more of a playing preference than a finely-balanced option. +science is always going to be pretty killer regardless of which resource you give up for it, etc.