My first landing at KSNA was 1974. We parked the Citabria just off the threshold of what is now due east of 20L, a bit east of the taxiway in question. Landed there many times since, visiting my office, and a g/f. Back then, we were allowed to take off from the taxiway with 'pilot discretion'. I never landed on it, but I can see how it is done. I've also landed there in a Piper J4(rear seat), C-210N, and a few other things. I've made one approach to 20R, but broke off and switched to the left at request of tower(fairly common).
I don't think they should put piano bars on 20L. If we are going to be confused about 20L being a runway or not, the trouble with adding piano bars is now it may look too much like 20R! Even though it is much shorter and narrower. Also, it has had chevrons on it for decades, and of course the taxiway never had them.
Ford uses his toys on unimproved strips, back country strips, and all over the country in and out of narrow and short landing fields. The taxiway he was lined up for prolly looked like a mega-runway to someone used to the sight picture of an 1800'x25' paved or gravel runway. Given that he was in the Husky, and that he's landed the heli in unimproved areas, this may have thrown off his aim.
The last thing one wants to do at KSNA as a PPL is interfere with 20R that has major traffic from Al overcast(well, 737s anyway) planes. Getting run over on short final by a comm plane would ruin everyone's day. So - I always cheated to the left a little, even on quiet times, just so I would NEVER be a burden, or make a mistake of 20R for 20L. I think this might be fairly common with PPLs like myself, but it's only op-ed. If one cheats to the left a little, and rolls out a bit early from downwind, it might be easy to line up with the taxiway, and leave it at that - knowing you would not be interfering with 20R.
Having said all this blather, there is no excuse, and no matter his celebrity, we are all the same once we strap on the plane. A series of small mistakes along the way portend that he wasn't really up to the challenge of aviating at his best. If I had made this mistake(I'm not perfect), and were mid-70s age, I would call the FAA, prostrate myself, issue the most formal of mea-culpa, schedule proactive radio and landing training, take my 709 ride, and do anything they asked. I might also go on a SoCal radio or talk show and apologize to the fans and other pilots out there that he has to mollify to stay in the good graces and be allowed to retain his privilege for a bit longer.
YMMV, don't try this at home, contents have settled, and may cause anal leakage.