I find the Poles concept of marrying an AS90 turret to a K9 chassis as quite interesting.
There are two key components to any SP howitzer, the turret with its gun, its gun laying system and its autoloader (if any) and the automotive chassis. Within limits, the two are both interdependent and independent of each other.
There is no magic in a tracked chassis for artillery as off road manoeuverability, while important, is not as critical as for a tank or IFV. Mass is the issue and the ability of the chassis to carry the turret off road and to take the shock of firing while providing stability for the departing round.
The US is coming from behind when it comes to autoloaders which is not the same as saying they will stay there, but if one wants to have an SP turret which will be mass produced, regularly product improved and maintainable, one should either tie themselves to an M109/M1299 or K9 turret. All others are too low a volume to be dependable for the long term (and we do go long term).
Weight is an issue if one wants to slap one of these turrets on a wheeled chassis. Our current LAV6.0 comes in at up to 28 tonnes. The Boxer comes in at up to 38 tonnes. The current M109A7 at 38 tonnes (without autoloader - the M1299 should be more due to its longer/heavier barrel and mount), and the K9 at 47 tonnes. The Kraus-Maffei AGM module which goes on the experimental Boxer SP is 12.5 tonnes. So one roughly needs to expect the chassis to carry and power lets say 12 to 17 tones of gun turret and absorb firing shock.
The HEMTT comes in at 20 tonnes unladen and is rated at 10 tonnes cargo. Our current HLVW is rated at 10 - 16 tonnes. Both are a bit light but are coming in at the very lower end of what is needed. Guns like Archer and Zuzana 2 are pointing the way. We should really examine the Ukrainian experience very closely as to how well they bear up under combat stress.
There are a lot of wheeled chassis SPs out there right now and more and more being built every day. Wheels appear to be a viable solution but, for me the issue is turret first, chassis second. Let's make sure we can find a gun, a gun control system (especially one that can tie into a standardized division wide fire control networ) and an autoloader we are happy with and then either buy an existing chassis or graft it onto something that we can easily support. One thing is for sure, the M777 barrel at L39 is too short for an SP these days. We're basically talking L52 as a minimum and probably more like in the L58-L60 range. That takes a chassis with some mass.