It’s incorrect to assume that SysEx is something basic, given that this is specific for every manufacturer and product, so there’s no single standard definition. Also a lot of devices are using checksum bytes which must be calculated correctly, that means Midihub would have to be aware of the many different variations of this algorithm that is in use by different manufacturers and products, as long as you want to be able to use variables within the SysEx data.
We are aware of this feature request, but there’s still things to do before we get there. 