There's a German term I'd highly recommend for a career as an international loan word… the eierlegende wollmichsau (egg-laying wool-producing milk-giving sow) – a jack of all trades but master of none sort of imaginary creature. Budget constraints have given birth to many eierlegende wollmichsäue over the years, all marked by cost-overruns and most by unkept capability promises.
On due deliberation, surely it would be better to develop two different vehicles then and just co-produce technologies and parts that can go into both. The weapons and sensory equipment, the armour technology, the engine and so on spring to mind.
After all, you do see a lot of MBT 70 DNA in both the Leopard 2 and the M1 Abrams, and though the vehicle got cancelled it helped to lower the development costs of the follow-up projects. Imagine the same trajectory, but under common management. The tax payers of both countries could save a lot of money.