It was an exciting trip even if I only experienced it from my comfy chair without any struggle breathing.
Here's the thing, most people would be able to complete this hike, even though it is a challenge. It is a mental challenge and not really a physical one, even though in many ways your body is affected more than your mind is. If you have a good guide, acclimatize properly along the way, and alter the itinerary if/as needed, then it's "simply" a matter of performing the required number of steps, one step at a time. Once you land in Lukla and start walking, only extreme circumstances will set you back enough to warrant you to abandon the hike and turn back: significant high altitude sickness symptoms, a twisted ankle (or something similar), or some (unrelated to high altitudes) medical condition such as a stomach viral infection (this is why most hikers will not touch meat on the trail). Yes, almost every single step you take feels like it's your last one, but you learn to get through that. Nobody turns around because they get "too tired to finish". You just keep going. It doesn't matter if you're the world's top athlete or an extreme couch potato, this is not a technically challenging trail. You do it one step at a time, you acclimatize properly along the way and pay attention to symptoms, you take care of yourself and getting to Base Camp is not a problem. Yes, you'll feel like you walked through hell to get there, but everybody on the trail feels the same way (except the Sherpa)
I saw people of all shapes and sizes on the trail, from the very old to the surprisingly young.. from slightly oversized hikers to overly thin to people with all sorts of expensive gear, to hippy looking people hiking with the bare essentials. You see everybody on the trail, although everybody there does have one thing in common: they went out of their way to plan such a trip.
I am saying all this in case anybody looks at this thread, thinks of maybe doing a hike like this.. but gets discouraged since it seems like it's something that only crazy or athletic people do. Not the case at all! I would bet you $100 that at least 75% of all posters here would be able to complete this hike. I assume that some people might have underlying medical conditions, some might have knee problems and can't do long hikes, there's hip issues,there could be high blood pressure problems (raises hand), etc. But if you can walk and aren't obese - you can probably do this hike. There are people who want to go there but only walk to Namche Bazaar.. They look at the itinerary and think "Wow, 2 weeks, that's nuts! But 4 days, why not? Namche Bazaar seems close to the trailhead". But each one of those people will always be overwhelmingly told - If you get to Namche Bazaar - you keep going. It makes zero sense to turn around and head back to the airport at that point. When you're in Namche Bazaar you will no doubt climb to that acclimatization point @ 4,000m, because that's a great spot to spot Mt. Everest from. If you do that.. You keep going. In some ways you are already halfway there, as weird as that might sound. Yes, there's still 6 days of hiking to get to base camp, but you've already completed 1 of the 2 (pretty much required) acclimatization/rest days. You don't stop there, it makes no sense!
All that is meant to say - if you can walk 2 days to Namche Bazaar the you will be able to keep going and walk to Base Camp. And most people will be able to walk to Namche Bazaar. The high altitudes really kicked my butt during the approach to Namche Bazaar, which is uphill walking for the last hour IIRC... but you power through that. Along the way you'll learn that your mind and body are far more resiliant than you've ever given them credit for. It's a phenomenon we couldn't stop talking about on the trail. Every day, you just go.. step by step.. you power through it and you'll get to the next teahouse. Step by step and eventually you'll be at Base Camp.
Admittedly we deviated from the classic Base Camp Route on the way back - and crossed that alpine pass so that we could return a different way. This alpine crossing is technically demanding to a small degree. It was the sketchiest part of the whole route from our pov. It's slippery, you're walking on ice and snow, and there's a drop down to a glacier on your right, for a while. Then the descent is fairly steep and you have to always make sure to properly plant your crampons. There's rocks and snow and it's just tedious to walk in the crampons, especially as the lower you go the more rocks become a part of the terrain.
What I said about almost anybody being able to finish this route, I am talking about the classic Base Camp route. Throwing the Cho La pass into the mix gets a bit more tricky. The classic route is basically very.. pedestrian. The alpine crossing feels a lot more raw and dangerous. It's not really that bad, but we didn't have high altitude alpine crossing experience at all, it was all new to us. Our Sherpa friends found the crossing rather pedestrian. But that's their pov.
I guess I wrote this wall of text to try to encourage people to think of doing this hike. Almost anybody can do it, it doesn't have to be expensive, you end up seeing some amazing scenery, and the local culture and the local people will leave a lasting impression on you. The one thing I would make a note of is your medical state of being. If you have high blood pressure or heart problems I would consult a doctor before going.