Hawala has kinda been out there for a long time, and I'm not sure that there is a space for incremental improvement since, as I already mentioned, its main security properties lie in hawala being out of modern fully electronic systems. This is the case when we are talking about the general mechanism, of course; a group of 2, 5, 10, N people | N < some abstract big number where we can't tailor solutions easily and need to scale, there some customization may surely be devised as an improvement.