A 'realistic' neurohelmet and Mechwarrior gear would be a very different thing from.
I'd think it, and all the associated gear with it would be this strange hybrid between a modern jet pilot/F-1 racer and super-bikers get up. A visor would sure as hell be polarizing, they'd probably have a faceplate with eye peices with polarise as needed and also act as the HUD, a breath mask would probably be included and they would be strapped in tight to their seats, with clips and restraints as well as a version of the HANS device - https://en.wikipedia.org/wiki/HANS_device that racing car folks wear.
I'm not sure I see the need for a closed face in this case. While mechs can operate in a variety of hostile environments, unless the rest of the pilot suit doubles protection, having an air supply may not be worth it. On the other hand, just having a cool breeze over the pilots face would probably be a welcome comfort. And just to throw this out there, if the canopy polarizes, why bother with polarized lenses on the helmet? Why add the weight? "What if the canopy blows out?" Is the limited functionality in a relatively small set of circumstances worth the discomfort an extra 6 ounces will cause the wearer the other 99% of the time? I don't know.
I agree 100% on the need for a HANS!
Add onto this on the cooling suit you'd have probably armour plating on the front and back of the chest (kevlar or space kevlar or something) to protect against spalling, as well as on the insides of the thighs to protect arteries.
Well, first you need to move beyond gym shorts as a piloting uniform. :-) As long as you can regulate the body's core temperature, the limbs will take care of themselves, so in a sense, a cooling suit
may not be a significant improvement over a good vest. That said, if cockpit fires are enough of a threat to wear fire proof boots, then why aren't you wearing a nomex flightsuit over your cooling vest?
FedCom cooling vests were described as being "ballistic nylon," and Kai survived a couple gunshots on Alyina. A few other lines suggest that it's a fairly flexible armor, compared to modern "soft" Kevlar vests. So added protection to the legs and groin is certainly a good idea. You could bias the protection to the front and sides if you take a cue from modern combat helicopter design and make the entire seat out of protective armor. There's an inch or more of Kevlar plate along the sides, back, and bottom of the seats on US attack helicopters. How much protection to give the arms is another question. You don't want to encumber them too much. You probably don't want anything much beyond nomex gloves on the hands because they have to manipulate controls.
Mobility would be restricted because the Mechwarrior's strapped in tight and the HANS systems holding them too. But this is better than having a Mechwarrior snap their neck the first time they fall over or get knocked over because of the huge whiplash forces involved.
The old school neurohelmets
do offer some head/neck protection.
I think it was Assumption of Risk but when Kai and Galen had a 2v2 match in Solaris. In addition to spiffy, form fitting cooling suits, wasn't there something about the neurohelmet's sensors being built into the suit's balaclava? And they wore regular helmets for impact protection.
Sarna mentions that neurohelmets are designed to pick up inputs from specific areas of the brain. While you can do this with an EEG, sensor placement is finicky, and that may not read the targeted part of the brain with enough specificity. I suppose the bulk of a neurohelmet might come from multiple arrays of sensors. The aggregate data is fed into an algorithm that builds a map of neural activity versus 3D position. If you are trying to detect small EM signals, you need coils, lots of coils. Star League and Clan systems can get by with a mix smaller, less sensitive, sensors, but use more of them, and rely on better signal processing. When I say "less sensitive," I mean compared to a Star League grade sensor the same size as a SW model. The camera in my phone has much higher resolution than my brother's 15 year old DSLR, but way less than a modern DSLR. So the bulky, heavy, Succession Wars neurohelmets
do make a certain amount of sense. That said, the art fro the old neurohelmets is just plain fugly.