I'll say go for it.
If ARC accepts your child, your child does have "easier access" to Pathlight school if he has difficulties in mainstream pri school.
And possibly Eden School as Pathlight runs both schools.
From what I know, the queue for higher-functioning kids is short. The wait is about 2-3 month, like what you mentioned.
Historically, selected kids do well in their programme, ie they must think your child can do well; otherwise the wait may be 12 month or forever.
ARC/Pathlight does require close family/parent support.
There may be adjustment problems. You will have to see if your child can cope with 2 methods of teaching. Asperger or high-functioning kids do better with a mix of approaches. ABA-based curriculum is recommended for children with more severe behv issues or who are at pre-communicative stage.
I tend to think that any child, not just ASD, who is uncommunicative and requires full supervision in daily self-help may benefit from intensive ABA-type of curriculum. It is a very structured form of teaching.