Sending more than BUFFER_LENGTH(32) bytes in slave answer I2C
The limitation is purely in software. The I2C hardware has a limit of one byte at a time, and the software creates a 32 byte buffer and feeds each byte from that in turn.

While it would be perfectly possible to increase that buffer size, you may find you have other problems when you get above 255 bytes, since lots of parameters and internal variables for the library are limited to 8 bit values.

It would also be considered very "hacky" since you can't easily upgrade the Wire library in future.

A better strategy would be to split your data into chunks and make multiple requests, each one saying "Give me chunk number ..." and then recombine them upon reception.