[root_axis]

The theory as described in your link seems to hand-wave away the difficulties incumbent in the "colonization explosion" step. As it stands, intergalactic space travel (at scale) is utterly inconceivable in practical terms, and to simply assume that it is inevitable seems like a major flaw in the theory.

[idbehold]

> then it's more likely it lies in our future (e.g. global thermonuclear war, plague, difficulty of space travel, etc)

Difficulty of space travel is one of the possible filters.

[root_axis]

Ah. I guess I was responding to

> the only thing that appears likely to keep us from [colonization explosion] is some sort of catastrophe or resource exhaustion leading to the impossibility of making the step due to consumption of the available resources (like for example highly constrained energy resources).

[svachalek]

Actually, the article explicitly calls out that step as one potential "great filter". It also (click the link) lists the theoretical ways it could be accomplished.

It seems to leave out the Von Neumann Probe:

https://en.wikipedia.org/wiki/Self-replicating_spacecraft

This is not exactly colonization but possibly an easier step. Either way, the point is that if either we or our machines can get to another star system and repeat the process from there, exponential growth means it pretty much doesn't even matter how long it takes. In astronomical time, we'd cover the galaxy in the blink of an eye.