David, if I had to choose one goal for everyone, it would probably be "b"; they're all doable, and most everyone can accomplish more than one, but I really think for most people, that's probably the best all-around one. Be warned, the following is going to be long, feel free to just go with "yes, just do the PM" as your answer; remember too, sometimes it's okay to make the PM a 5 or 6 day program; Pavel has a great 5 day variation that's been posted.
Regarding your question, in my experience, the answer is "it depends". It is absolutely achievable by just doing the PM as written continuously, whether that's the best or fastest (not always the same thing) path to the goal depends on the individual, but it will definitely work, and would be my default recommendation. I will say that I have a few different approaches to progressing with swings that expand upon what's written in ETK, but in my opinion, complement rather than contradict. For instance, double swings sometimes fit in here. Here are some the things I take into consideration with individuals that I've worked with; this is more about when and why I add to the PM, because it's easier for me to conceptualize, but the same basic reasoning and process applies to whether I advise people to cycle programs or not:
a) What other physical activities and sports do they do? I ask this for a few reasons:
1. How much do they have to recover from (and, what's their recovery ability)?
2. Where does this fit in to their overall life?
3. Are there other movement patterns or skills or qualities we want/need to address? Be careful with this though, as it is really easy to go way overboard and clutter up the PM to the detriment of the program. Remember, as Dan John says, "the goal is to keep the goal the goal"
b) What other resources are available to them?
Deadlifts can be a great addition to the PM, so can pull-ups. If someone doesn't have access to a barbell, there's no point in me recommending them. Ditto if they can't reliably get to a pullup bar. Seems simple, I know, but this seems to get ignored/argued about a lot on forums. Work with the tools available.
c) What's their interest, and what do they have fun with?
This is an important one, that often gets ignored. People will be a lot more motivated, and often get more out of, things they enjoy doing. This could be expanded on a lot, but suffice it to say, if there's not some serious goal, like making the olympics, or making a living as an athlete, fun is important, imho.
d) Which is harder/what are their weak points?
Some people come to me with a background that's going to predispose them towards get ups more, and will progress faster on these, others will pick up the swing a lot faster and progress more easily with that. I could write a very long post just on this. Preferences are fine, but I like people to not have too much distance between proficiency in both, so if they're doing getups with 32kg for time and struggling with swings with a 16, something's off. If I'm going to supplement the PM with something (and at the risk of repeating myself, I don't always by ay means do so), I look at what can I do that will bring up the weaker half without compromising the stronger half.
e) Look outside the box:
While I will often use things that would be familiar to all of us (e.g. deadlifts, pullups and other bodyweight exercises, goblet squats etc) or variations, often times I find the best thing that a lot of people can add is either a good qigong or yoga practice (and I emphasize good, as there are a lot of terrible teachers of both, just as there is Jillian Michaels in the kettlebell world) and/or a meditation practice (I'm partial to a couple of approaches in particular here). There's a lot of ways in which that can be of tremendous benefit to a lot of folks in the strength training world, and I find they are often missing.
Hope that's of some help, remember, it's also fine and wonderful to just do the PM as written!
