I believe that you are seriously over interpreting there. The suttas talk about not having self view in the past, present or future, not that you can't think about the past, present, or future. Where does it say: "keep all thoughts of birth out of your mind"?
We are not stream-winners or arahants (sorry if anyone is) so any view/question about past or future is going to be coloured by self view or conciet and so such views and questions will just increase ignorance and the taints (also they are asking the wrong questions anyway). One cant help but put "me" or "I" in the future when ignorance hasnt been removed.
So the Buddha advised not to have or ask such speculative views/questions since they reinforce delsuions (they all come to be via having self-view anyway) instead he taught to focus on what is (4nt) to remove all delsuions and dukkha. When this is done such speculative questions/views wont arise in anymore anyway since one has seen
As i have said, the Buddha taught that such questions are unwise and only focusing on what is, is wise. Rebirth view/speculation naturaly involves such questions as
http://www.accesstoinsight.org/tipitaka ... .than.html
This is how he attends inappropriately: 'Was I in the past? Was I not in the past? What was I in the past? How was I in the past? Having been what, what was I in the past? Shall I be in the future? Shall I not be in the future? What shall I be in the future? How shall I be in the future? Having been what, what shall I be in the future?'
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You say it's wise to consider the cause of Dukkha. You have dukkha because you were born. But since your view is that the only definition of "birth" that can be admitted into Dependent Origination is the "moment-to-moment interpretation" you want to redefine things so that "physical birth" is something "speculative".
The Khandas are void of a self, the only "birth" of a "being" is that perception which arises in the mind due to ignorance and clinging. The physical birth of the Khandas is not "my" birth, the birth of "me" came during the first time there was clinging to the khandas (and so birth of identity, identification through "I am).
The Khandas arent dukkha, clinging to them is
"Now what, friends, is the noble truth of dukkha? Birth is dukkha aging is dukkha, death is dukkha; sorrow, lamentation, pain, distress, & despair are dukkha; not getting what is wanted is stressful.2 In short, the five aggregates subject to clinging are Dukkha
To say "my" birth is clinging, when there is no clinging there is no identification and so there is no birth, ageing, sickness or death since this comes to be via clinging and identification "I was born, i am ageing, i will/am dying" and all the dukkha that comes with that as well
"There is the case where an uninstructed, run-of-the-mill person — who has no regard for noble ones, is not well-versed or disciplined in their Dhamma; who has no regard for men of integrity, is not well-versed or disciplined in their Dhamma — assumes form (the body) to be the self, or the self as possessing form, or form as in the self, or the self as in form. He is seized with the idea that 'I am form' or 'Form is mine.' As he is seized with these ideas, his form changes & alters, and he falls into sorrow, lamentation, pain, distress, & despair over its change & alteration.