Conventional intensity modulation and direct detection passive optical networks（IMDD PONs）have limited flexibility to cost-effectively accommodate a large number of emerging applications with largely diversified requirements in terms of bandwidth, latency and connectivity. To effectively address this technical challenge, a novel Inverse Fast Fourier Transform/Fast Fourier Transform（IFFT/FFT）-enabled Point-to-Multipoint（P2MP）optical transceiver has been recently proposed and experimentally validated in upstream IMDD PONs. However, comprehensive investigations of the flexibility of this technique are still required to validate its suitability for future applications. To this end, by using presentative upstream IMDD PON simulation systems, this paper first identifies the optimum parameters and then investigates the transceiver’s flexibility and resulting upstream transmission performances. Simulation results indicate that in cases where the optical fiber channel attenuation is not significant, the fiber transmission distance can be flexibly adjusted without significantly reducing the system transmission capacity. In addition, each ONU can flexibly change its channel count without significantly reducing transmission capacity if the channel counts are≤10. Furthermore, by dynamically changing each ONU bitrate, each ONU can flexibly alter its ONU launch power dynamic range.