The situation is that the so-called type zero and type one conditionals are either not worthy of the name conditional, or if they are then they are definitely in the realm of realis/not subjunctive.
The irrealis conditional with subjunctive really kicks in with the "type two".
Past subjunctive (past simple subjunctive) is exactly the same as past simple (past simple indicative) except that in all persons the past subjunctive of "be" is "were" (for the time being).
So all these are past subjunctive:
I wish it were still summer.
It's time you went.
I'd rather you didn't
If only you spoke
If I came tomorrow
In other words all those uses of the past simple that simply didn't happen in the past.
The origins of this are that, like those cognate European languages which still have a past subjunctive, English once really did:
fremman (weak,regular) 'do' helpan (strong, irregular)'help'
present indicative iċ fremme iċ helpe
past indicative iċ fremede iċ healp
past subjunctive iċ fremede ic hulpe
http://www.wmich.edu/medieval/research/ ... lverb.html
so the weak past subjunctive was the same as the past indicative, although the strong past subjunctive was different. At some point that subtle difference disappeared though "thou wast" and "if) thou werst" lasted a bit longer.
Even if "If I were" disappears then it''ll stiil be useful to differentiate between past simple and past subjunctive, otherwise "If I sold the milk tomorrow" will take some explaining.