What one would do would be to gradually work into the lower rep ranges reducing total volume (weight moves up, reps go down - lower volume).

It's not like gains in your 3x3 and 1x3 won't push your 1RM up substantially. I would really caution you to just run it as is the first time through - there are a lot of ways to do this program but I've found that people unfamiliar with this type of training screw it up and as they are isolated over the internet. The volume is part of the stimulus and it works fairly well for pushing the weights up. For straight PL though there are other changes that would be made as this is more general conditioning rather than PL specific. If you wanted to peak your 1RM, you'd go from triples to doubles to a period of heavy singles with low frequency/volume and plenty of rest at which point you'd perform your 'records' or do a PL meet or whatever. incorporating 1rms would be ideal though. I was just thinking of making everything for a 3rm rather than some for a 3rm and some for 3x3.

Bill starr 5x5 excel spreadsheet