I've built around 600 saws, give or take 20, in the last 15 years. I've tried every configuration imagineable, including removeable heads. When you make engine components separate, i.e. removeable head, that allows those components, even if they're made of the same material, to expand and contract at different rates. Even a one-piece jug expands more at the compression ring than it does at the base. This is one reason why the bore is cylindrical, rather than a straight tube. As for retarding the exhaust you recut those figures by raising the exhaust port, and advancing the intake timing is a desirable thing in a modified saw. Plus, if a user wants to go back to using a stock piston in one my saws, it's not a problem- simply return the stock base gasket under the cylinder and install a stock piston. I don't run tolerances so closely as to totally void any stock design. You need to have at least .025" clearance between the piston crown and the compression band for a durable working saw, I run mine at .030". I've seen stock saws vary between .045" and .070".
The removeable head on a modern saw has already been tested by multiple users, saws that were built by high quality shops like Baughmann's and Walker's. The removeable head design on a small, lightweight modern saw just will not last as long as the original one-piece cylinder. Period. It doesn't dissipate heat fast enough regardless of your gas and oil set-up and it will not take the abuse of pro timber falling or landing use day after day, even if you make the CC twice the size of a standard race set-up. For a woods saw, simplicity is best. Keep the number of moving parts and bolt-together items at the very minimum. Talk to any saw builder, pro or semi-pro, and you'll get the same answer.
As for the 'pop-up' part of this set-up, it does not hinder scavenging in any way. In fact, it helps exhaust scavenging slightly and also helps the spread of the charge after firing.
Many manufacturers have been making factory domed pistons for years- Stihl 028 Super, 024 Super, 026 Pro, MS 260, 038 Super, 045 Super, 056 Super, 056 Magnum, Sachs 143 and 166, McCulloch 44 Super, Husqvarna L-65, 285, Partner R-7000 to name a few models.
Here's another thing you've missed- anytime you lighten the reciprocating assembly, within the allowable inertia requirements to keep the saw running at an idle, you make more power available for the saw to produce at the PTO, because the engine is doing less work to function. There's a balance you have to strike in there to be sure, but less weight is better in a smaller, high speed engine. That is if you don't compromise the structural integrity of the assembly. Older saws, especially gear drives, used heavy pistons and cranks with heavy throws to maintain intertia which helped develop more torque at a lower RPM ( and big, heavy flywheels too ). Modern saws rely more on the power of combustible fuels and higher flow rates to develop horsepower. Another thing to remember is that modern saw cylinders are very thin, unlike 2-cycle engines in other applications- motorcycles, watercraft, pumps, etc.
The older saws like the Macs had thick, heavy cylinders and crankcases which left more room for error and design flaws among other things. McCulloch, Homelite, I.E.L., and Mall all tried various ways- starting with a design much like modern saw production- 2 crankcase halves with a bolt-on cylinder. Then they moved to the crankcase halves, bolt-on cylinder, and bolt-on head. Then they went to the intregral cylinder/crankcase one piece design, like a Mac 795- and with that some used the bolt-on head with the integral one-piece cylinder/crankcase like the kart engines. Eventually all saw makers went back to the crankcase halves and bolt-on cylinder design, both for cost and durability. Not all manufacturing decisions are exclusively based on profit concerns- they have to make a somewhat durable product so people will buy their stuff.
I think Stihl hit on the ultimate big saw design with the 090- The main portion of the case is one-piece, except for a small bolt-in part which housed the electronics, flywheel side roller cage bearing, and is supported by five long studs ( 30 and 45mm long ) and two heavy dowels ( 36mm ). From there you lined up the crank ( which was supported by 30mm long needle rollers ) and bolted on a one-piece jug, which mostly had four base screws but a small production run had six base mounting screws because some guys were porting the jugs so heavily that they blew the tops off of them. There were also a small run of 070 and 090 saws that had domed pistons from the factory.
From the stand point of resleeving ,or porting,a removable head,is much easier,I can tell you from experiance.As far as the kart engines,a stock 125 is 7.5 to 1 compression ratio.A 101 ,is 9.5 to 1.Back in the kart days,they just installed a Wiseco ,high comp piston,and recut the ports.Most serious karters had several engines,because they would only be good for about 10 or so races,if that many.I would say that a racing 101,would not last on a saw,that is used hard,for very long,but while it ran,it would sure eat the wood. 
