Not sure I follow.
If the venue in which that successful engine design stops, the design becomes invalid?

You can see them in Comp Eliminator.

A friend of mine has(had?) A 3.91 stroke 4.375 bore hemi that accidentally hit 9800 rpm last outing. Both valve heads in one cylinder went through the piston. Kinda made a mess. The valvetrain failed first. A Hemi spinning 7500 would be a challenge in the valve train department. 10,000 rpm would be insanely expensive.

JESEL or T&D would eliminate some RPM issues.

I read an interesting article that detailed a lot of what went into a 9800 r.p.m. SS/AH motor and it was pretty remarkable.
Narrowed cam bearings and re-located lobes was the part where I physically felt my wallet cringe in my back pocket.
Spreading the lobes nearly 1 " also required custom bedding and rocker arms , and had to oil the valve gear through the push rods.
If you can dredge up a February of 2011 MoPar Action , it is pretty interesting.
And 8 years old. God only knows what they are doing now.

Charlie Wescott moved the lobes around first, to try and straighten out the push rods. He also creatively interpreted the rules in regards to milling the intake flange, they later changed the rules

Assuming using a stock block?
Keeping the block & bits itself intact is the easy part: spend money.
The rest is partially money: 7mm valves, biggest double-tapered pushrods that will fit, titanium? collars, beryllium? springs, Spintron test everything.
Offset secondary rockers as jackshafts to correct pushrod angularity have been used successfully (but not in race cars, or recently).

The interesting part, to me, is to force someone to run an FEA program on the Barton rockers to isolate where mass can be safely removed without structural compromise, which may take many passes to get the lever ends slimmed down (as we say "make it all the same blue color"). Once this is done, no brain surgeons are needed, a small boy with a Dremel can duplicate the work. Wouldn't it be nice if Barton donated a (slightly used) set, in exchange for valuable data he may not have?

What does a really long rod ratio do to vacuum?

The bikes are a very short stroke. A few years ago I sold my Suzuki GSXR750. It would rev to 14,300 before it would hit the limiter and your could do that in neutral without hurting it. It had a 1.9" stroke.

Really stalls piston motion B/ATDC, initiates vacuum later, reduces piston to valve clearance. This is acceptable for an engine with small ports + large displacement (or no need for low speed power, like F1), but kills torque if the engine size drops. The opposite (big ports and short rods)? BBC, works very well.
Reducing engine size by bore change is almost harmless as long as the new wall position does not significantly shroud the intake valve. By comparison, reduction by stroke change, even with reduced deck height, seldom does what you want.

New Honda CBR1000rr is 13:1 compression , turns 13k rpm and runs on pump gas . I see the new Mazda Sky-Activ pump gas motors are up around 14 and 16.3:1 compression ratio.

Yeah, mine was 12.5:1. Dont know how they do that on pump gas.

Anyone know what the ignition advance curve looks like on a bike ?

I added a power commander to mine which controls the fuel and timing. All I know it that every gear has it's own fuel and timing map.

Those mazda's are kind of cheating when they say they have 16 to 1 or whatever, the fuel is directly injected into the cylinder after the piston is coming back down and the cylinder pressure is not so high as well as cam position being manipulated to increase or decrease overlap and retarding the intake valve timing to reduce cylinder pressure. At part throttle when cylinder pressure is reduced by the throttle restricting airflow then it may be injected closer to or even before TDC butt again, cylinder pressure is not as high under those conditions.

Motorcycles run high compression as a result of a typically very straight shot of cool air to the cylinders with very minimal if any heating of the air as well as small bores that tend to ward off detonation and very large cams that bleed off pressure. The individual runners also tend to run much smoother with a very large cam than multiple cylinders running off a common plenum with a huge cam, the cylinders are not interfering with each others air/fuel charge. Remember too that 1.9 inch stroke is not moving the piston any faster at 14,000 than a 3.8 stroke at 7000, twice as many cycles but nearly equal average piston speed. It is hard to compare a motorcycle valve train to a pushrod engine, the cam is usually pushing directly on a lash cap/tappet thingy with no pushrod or rocker arm weight to deal with at all and none of the weird harmonics that need to be dealt with that are associated with them.

1.9 inch stroke is not moving the piston any faster at 14,000 than a 3.8 stroke at 7000

But the peak piston acceleration is much, much higher: Z (in feet per second, per second acceleration) = (N^2 × S (1 + (1 ÷ 2n))) ÷ 2189
(assuming 2:1 rod ratio for both engines)
1.9" stroke @ 14,000 RPM: 212,654 f/s/s
3.8" stroke @ 7,000 RPM: 106,327 f/s/s

Many current DOHC auto engines have variable valve timing, which uses... rocker arms. 2JZ (Supra) owners don't seem to understand what that is.