This article proposes a scalable integrated system architecture modeling for hardware accelerator based in gem5 simulation framework. The core of proposed modeling is a LLVM-based simulation engine for modeling any customized data-path with respect to inherent data/instruction-level parallelism (derived by algorithms) and available compute units (defined by the user). The simulation framework also offers a general-purpose communication interface that allows a scalable and flexible connection into the gem5 ecosystem. Python API of gem5, enabling modifications to the system hierarchy without the need to rebuild the underlying simulator. Our simulation framework currently supports full-system simulation (both bare-metal and a full Linux kernel) for ARM-based systems, with future plans to add support for RISC-V. The LLVM-based modeling and modular integration to gem5 allow long-term simulation expansion and sustainable design modeling for emerging applications with demands for acceleration.