Physical expertise required!
I didn't bother to read up on the science, but the thing you discuss is nothing else than using polarization as an extra degree of freedom for data transmission. Unfortunately, El Reg / the author has failed to grasp the rather simple physics behind this story and therefore offers a lot of very unphysical comments.
"Orbital angular momentum in waves is difficult to explain, because frankly, any non-mathematical explanation is at best an imperfect metaphor."
No it's not difficult to explain: If you add a beam with polarization in the x-axis and another with polarization in the y-axis (the z-axis being the propagation direction), you get a 3-dimensional wave in space and time. Upon modulation of both signals, the resulting wave may look quite complex (e.g., producing a helical wavefront), but the signal can always be decomposed into the x and y polarized components -- quite simple really. Everything else, including the moniker "orbital angular momentum" is spin, not of the physical type, but rather of the advertisement type.
"El Reg notes that while OAM is hailed as offering “infinite” bandwidth, it’s limited by how finely “spin” can be manipulated and detected. It is, however, a very young technology."
Photons have no spin, neither does any other electromagnetic wave. The angular momentum in the polarization shaped beam adds information density relative to a linearly (or circularly) polarized beam. Indeed, the information content is easily established because any helical polarization can be created as the sum of two linearly polarized beams. The information content is therefore exactly twice as large as that of the linearly polarized case. Apart from that, the information content is a question of bandwidth -- and this in principle infinite if you assume that you have emitters / receivers with infinite bandwidth. Nothing new here.