I've wrestled with this, personally. Honestly, I think it's hard to tell what's viable and what's not when it's your baby, and you've been living and breathing it for months.

The standard that I hold myself to is whether or not the product provides value to the user or customer. Does it do something new or interesting that someone (besides your team) cares about, or is it just the first part of something that you hope will provide value? It's tempting to jump the gun, and I think honesty on the part of those around you can help keep you from releasing a minimum, non-viable, product.