We've had the technology to publish science online for decades. We have tinkered with it dozens of times. The web was originally invented for exactly this purpose. Far older things, like TeX, were invented for this purpose. Nowadays we have everything from PLoS to arXiv to Google Scholar to custom in-house blogs to PDFs sent through email.
The continued existence of for-profit journals is an economic, political, and anthropological problem, not a technological one. PLoS and the like are slowly changing things, but I still suspect that the only way to free our journals within less than a generation or two is to lobby (e.g.) the NIH to require that their funded projects be published in free journals. When a grant agency talks, people listen. When postdocs talk, alas, it makes a very subtle sound. ;)