I would not call that unrealistic. A few comments:

(1) Only on HN would anyone dream of referring to your list as "everything". You are actually targeting a very narrow, focused skill set: those required for a small(-ish) software or software-intensive business. Like it or not, you're proposing becoming a specialist (albeit with a somewhat broader specialty than a typical job description would call for).

(2) In the real world, "everything" includes many, many other things. To get good at all that stuff on your list, you'll need to leave other skills by the wayside. The comment by taprun mentions chess, running, and cooking. You won't be getting better at any of those.

(3) The I-do-everything approach sets a hard limit on the size of a business. An important reason for hiring & delegating is so that a business can grow.

In economics, I learned about something called a "trade-off". Basically, if you spend time learning something, you are spending that time not learning something else.

I remember meeting someone who was fantastic at chess. He destroyed me. Repeatedly. My mental model of him was essentially "me but good at chess". It didn't occur to me until much later that he didn't know how to program a computer, couldn't run a mile without stopping and didn't know how to cook Chinese food.

I think if you stop seeing people as "you but can do X", these feelings will go away. Alternatively, read up on the concept of "comparative advantage" and realize there is a mathematically proven reason not to try to be an expert at everything.

This is largely the same goal that I've set for myself. I spend a good amount of time doing each (less marketing lately, more towards coding/design), and find that while I outpace most people in these fields, there's always people who specialize even further and know way more about them than I do. The trick is to spend as much time learning from these people as you can. I talk with my direct superiors at work a lot, because they're both insanely knowledgeable engineers. I also have some buddies that do full-time marketing, copywriting, design, etc, and each of them are constantly teaching me things. Make a point to regularly associate with a wide variety of deeply specialized people, and as a result, while you'll probably never be as effective as any of them in their given fields, you'll certainly be way more effective than most people. From there, pick one or two fields to use as anchors for your T (or W) shape, and then leverage that in your dealings with other fields.

Think of yourself as a pupa. Right now you're just incubating, you don't have to do anything fantastic, just learn and grow. Then, when you're ready, you'll break out of your shell and spread your wings :)

Of course, you can learn most of those things. However, it is my belief you will soon tire yourself. Getting to the top of everything is hard enough, staying there even harder.

I used to be up to date in a lot of domains. 3D modelling, app frameworks, web technologies, back end, front end. Those days, I find it's hard enough to focus on being up to date and relevant with front end web development while balancing an healthy life with friends and family.

You can do it, but remember that there is an upkeep to being relevant in a lot of domains. If you can deal with it, sure, go ahead!

However, what I would recommend you is a good team. I'm finding I connect easily with people that have complementary skill sets to mine, and it's a great experience.

Where did you find these people?

I don't think its unrealistic - the bar is just very high for what you want to do. Perhaps it may make sense to talk to people who would be looking for such an integrated skill set and find out which ones matter more than others and to what degree/level.

That will give you an automatic prioritization of how to go about getting these skills without becoming overwhelmed.