I think they were raising the possibility of having multiple reedits, each owned by a separate entity, yet still compatible. Like we have multiple email providers, for example.

Which kind of is the concept of reddit. What am I missing?

The each owned by separate entity bit. I think the earlier posters meant that if (somehow) a Reddit-like service was federated and anyone could set up their own server that hosted its own subreddits while sharing auth, it would be a very interesting product.

What would compatible mean? Why is compatability needed?

Reddit sucks for high-quality, long-lived discussions.

Of all places, G+ does reasonably well at this, with a suitably selective group.

Mailing lists / usenet are still probably the pinacle.