Guess you'll find out one way or another.
The two piece steering shaft wasn't supposed to move like that, which is why it was held in place with those plastic "shear pins". It was only supposed to move in an accident. When I disassembled my steering column and shaft they were still intact (which isn't always the case), that motion was taken up by the steering coupler. I tried to replicate a system that would do the same thing, and the sliding section I used definitely slides easier than the factory two piece shaft. Or at least the one in my car at any rate.
I don't know that my solution works any better. I simply wanted to point out that there was a reason why motion in that direction was accounted for by the factory, whether it was overkill or not, and share my own solution to the "problem". On my cars I take movement in that plane into account, you're free to do whatever you like. Movement like that would be less in my car anyway, given the chassis reinforcement I've done. On a car without frame connectors, torque boxes, and "J" bars or firewall to shock tower reinforcements (ie, a factory car0, it would be more of a potential issue as there will be more flex.
I'm not a fan of drilling the steering shaft and adding a through pin. The tolerances on that need to be precise to prevent slop and wear, and I suspect that most people don't take the necessary level of precision. Again, that's something that might not immediately be a problem, but if you put enough miles on the car it will eventually show up and someone will have to deal with it. There's enough potential for play in the steering system already, without adding more from "simple fixes".
And not drilling a through hole for a pin is even worse, if you use a round-round u-joint and just drill a small recess for an allen screw and lock nut that's all that keeps the steering shaft from spinning in the joint. No thanks. All the modern stuff uses "D" shafts so nothing has the potential to spin, even with a failure.
I think some over-engineering in the steering, braking, and suspension components of these cars is healthy. After all, that's your control and safety equipment.
