Years ago, the self-improver route was pretty much the only way unless you went through the BOAC/BA training schemes. In those days (up to the 1980s), companies took responsibility for all training, and the costs involved in bringing a pilot up to the required standards were relatively insignificant. There was no real problem getting rid of those not up to scratch, either...
Time has moved on. Costs, which are now enormous, are the overriding factor, followed closely by minimisation of risk. The old informal system of selection by the 'old boy network' (which did a pretty good job of weeding out the no-hopers) has long gone, and has been replaced by more formal arrangements. The fact that some pilots still achieve their dream by the traditional routes is an anomaly, though a welcome one for those who make it this way.
The likelihood is that, for airline flying at least, self-selection will be effectively outlawed over the next few years, and you will not be able to get a licence simply because you have enough money and time to keep plugging away until you get the right result! Opportunities will remain for those who take a more roundabout way of getting to the airlines, but the business of getting a professional licence wil be further tightened in order to eliminate those with money but insufficient talent.
Even if no legislation is passed to enforce this scenario, I suspect that, in time, the airlines will make it a de facto standard by refusing to employ people who have not undergone a pre-selected, time constrained course of training. Not necessarily 'integrated', but certainly at least 'structured modular' - or whatever replaces both. The MPL, as referred to in a post above, may well be part of that replacement.
Scroggs