NodeXL is designed for ease of use and exploration of networks. Scale has been a secondary consideration.
RAM and CPU are definitely important resources for NodeXL and control its performance. Limits in Excel (depending on the version) are also constraints.
For very large data sets we recommend that users consider the more powerful tools like Python/NetworkX or RSNA or iGraph.
If you need a much more powerful machine for a short period of time I suggest exploring the Amazon EC2 service (aws.amazon.com).
We are always delighted when our users suggest new features and ways to use the tool: Thanks!