Thanks for the spice.
As far as I'm aware, in the sutta-based teachings to bhikkhus, there is no talk of practice in future lives for bhikkhus. If future lives were going to play a prominent feature in one's epic spiritual journey, it is odd that the Buddha would not mention it, or that no one would enquire about it to him. Odd that no one would say, "Blessed one, my faculties are weak. How should I best prepare for the countless eons of samsara that lie ahead so that one day I might attain stream-entry?" It sounds a ridiculous question to one who had read the suttas, but if uncalculable whatzits were accepted to be the order of the day, it would be a valid question.
I know there are some Buddhist traditions where people do undertake certain preparations in order to ready themselves for subsequent practice in subsequent lives. To the best of my knowledge, any explicit post-this-life activity is not mentioned at all in the Pali Canon for bhikkhus in training and is therefore very conspicuous by its absence. The underlying assumption that may be drawn from this is that they're to do their best now, and what will be will be, and that the goal can be experienced here and now by the wise. All presentations to bhikkhus relate to this life and the pursuit of arahantship (as opposed to other fancy alternative destinations), so by the scales used in the suttas, there is no basis I see for believing that "long and short" are referring to anything other than time periods in this very life... assuming there is Right View and Right Effort and so on. If there's no following of the N8P, that's when the talk of long periods in samsara comes up.
The extracts from the essay I provided a couple of hours ago demonstrate the lateness of these epic-timescales as applied to preparatory aspects of the spiritual path and back Bhikkhu Bodhi's earlier comments in relation to borrowings from Mahayana. These timescales are certainly anomalous and alien with respect to the Sutta teachings to bhikkhus.