If someone chooses to participate in the whole Powerplay mechanic and primarily focus on it, it seems to me that they are limiting themselves to a "hand full" of systems, is that correct?
Edmund Mahon currently exploits more than 1,100 populated systems with more than 2,500 stations between them.
Add to that an unknown amount of unpopulated systems, and once Horizons comes online Mahon has more systems and planets to explore than you could reasonably expect to explore for a really long time.
It's still quite a ways off of 400,000,000,000, but it is slightly more than a handful.
If you dedicate yourself to PowerPlay then yes, you won't get to explore the entire galaxy, but then again, with 400,000,000,000 stars in the galaxy, you won't ever manage to explore the entire galaxy.
Even if you limit yourself to populated space, you're still looking at more than 19,000 systems and a huge amount of unpopulated systems within, say, 25 light years of populated systems. Add Horizons into the mix and you'll definitely start to have problems if you intend to visit and land on each planet. Even if we make a simple assumption that you'll spend only one hour exploring each planet, and each
populated system has one planet you can land on, then once Horizons is available, you'll have to spend more than 19,000 hours just to visit them.
Let's make a further assumption. Let's say you play 16 hours a day doing nothing but this. Now you're looking at 1,187 days and 12 hours worth of game time.
If you start at 8 AM on January 1st 2016, you'll be done by 8 PM on March 31st 2019.
Incidentally, for Mahon the numbers are a **bit** more forgiving, because then you'll be done by March 7th, 2016, but that's not
quite true, because it assumes that Mahon won't expand into new systems in the mean time (and I'm pretty sure he will).
And keep in mind that these estimates are being extremely generous in terms of the time spent per day, landfall planets per system and the amount of time you'll spend exploring them.
Don't make the assumption that the populated bubble being tiny in comparison to the galaxy means that it is tiny in terms of the content available.