Would a visible light beamforming "telescope" be feasible?
Not in the way you think, no. 

Digital Beamforming works because the digital receiver is able to sense the phase of the incident radio wave; that phase is retained.

Photodiodes don't sense the phase – they only sense the intensity. 

Also, this requires the whole incident radio or light wave to be phase-coherent across its front – that's the case for laser light, but not for two random photons emitted from a huge fusion fireball, I'm afraid. So, the second requirement also falls flat. Generally, even non-laser sources of light have a coherency period – but the more different wavelengths contribute the smaller that gets. 

In TX, that principle works – if you feed a laser through an array of digital phase modulators (optical crystals with electrically adjustable refractive indices), you can build phase-coherent multiemitters. 

In RX, that might also work, if the received coherent light can be made to fall through a microscope objective, and then onto an acousto-optic deflector, you might, via modulating that deflector's state, be able to build a selective/phase-shifting summer, leading to beamforming. But: that's particle physics sized electronics normally, i.e. suitable for situations where you have a very strong laser illuminating very small points (in fact, I learned about AODs just today, and they're usually used the other way around: take one beam of laser, split it into multiple parallel beams, focus these, and trap quantums in the focus point. Cool stuff.).

Anyway, there's also mathematical accuracy limits to digital beamforming, and I'd must admit that I don't know whether they'd even allow higher precision with the kind of timing accuracy we can do today. Then again, phyisicists invent the coolest devices, and maybe you can