I plan to do training plans one after another … indefinitely. I will time them so they end just before my annual 2 weeks holiday abroad, and start straight after. I do no exercise whatsoever during my 2 weeks … is that enough true rest per year? I’m increasing ftp by 2w per month approximately, and would like to see if I can continue that for another couple of years.
As each plan has recovery time built-in, I would think you should be fine. If anything, you’re likely to see your FTP decrease during your 2 weeks off, especially if you’re not doing any activity during that time, but you should be able to build it back up without much difficulty.
I think the real key is making sure you respect the recovery weeks in your plan, and not continually choosing the demanding or aggressive approach.
I would definitely take an off season at some point, it’s good to rest yourself mentally and physically.
But it depends how much volume you are averaging as well.
too much 
Are you training for general fitness to be in shape year round or have a defined season with a specific “A” race? How many days a week do you train?
If you just want to be fit year round, I would think the 2 week break is a good reset, though you might also benefit from a shorter “mid-year” break as well (even if it is a week of noodling around on a mountain bike or beach cruiser). If you follow the 3-weeks on, 1 week recovery as TR has them, it is a decent drop in stress with no intensity. You can pretty much go forever with that much recovery planned in.
If you have a specific A race that you are really ramping up for I am a big fan of time off following that event (no matter where it falls on the calendar). Even if you feel good physically, mentally you need a break and time to decompress after being on the gas for months.
I really like the 2 weeks away you have planned. Personally I like riding my bike cool places and bring it with me whenever I can (actually plan where we stay on trail access). That said Though I was thinking we should probably go on a vacation where I leave it at home. I guess for you it comes down to how hard are your training and what your rest looks like the whole year. What does your gut say?
I have no plan … or aims … or targets …. just aimless cycling in the absence of anything better to do (a good metaphor for my entire life haha).
I think the post above covers it really well. If you enjoy your current approach, stick with it. If it starts to get stale, you might try putting a date/event on the calendar and target a peak. A peak/push would likely get you to new levels, but isn’t sustainable. Doing these peak/break cycles is the classic “2 steps forward, one step back” and that approach can often be the path to higher fitness.
I am very much a fan of the +2/-1 approach. Or +3/-1 or whatever works for you. For me, obsession with constant forward progress is a recipe for burnout. I think of it like taxation; I don’t get to keep 100% of those gains. To keep my head in it I have to give, say, 10-20% of my gains back to recovery or pleasure to keep my enthusiasm from waning. Without joy the watts are just angry numbers, making me hate my bike and fear my sessions and resent the whole process to say nothing of the cumulative fatigue.
So I gain 5 watts in a 3 month block. Great. Fantastic! Now I’ll take a week off, ride my bike less, rest more, faff around in general and just enjoy the lack of structure. When I start up again I’ve lost very little fitness and it comes back fast and I’m off to the races again with a refreshed attitude and rested legs. That gives me at least 3-ish extra weeks “off plan” a year plus a proper off-season of a couple weeks. I stay fresh and it stays fun.
Good luck.
You will increase your chances of being consistent, and therefore getting fitter, if you do set some targets, aims and plans.
You can always change you mind later, so no worries planning the next three years with only six weeks leave, not following a structured training plan. I suspect you will change your mind in about six weeks though.
I’m guessing you’re young or new to endurance sports?
Burnout will make 2 weeks off feel like a split second. 
For me when training most of the year I’ve been doing 4 -5 week just split in two.
At the end of the CX season I’ll take three weeks off where by this point I don’t want to think about a Vo2 or Anaerobic workout anymore.
Then usually some time during the season, against my wishes I end up going on holiday with the family.
They both help physically but mostly mentally.
For the family holidays I usually take some running shoes with me so that I don’t feel like I’m missing out too much.
Nearly 49. Been cycling long distances for 35 years. Sometimes I have targets (70 miles at 14, 1000 miles at 30) other times its just a way to switch off or prove a point.