No. As a reseller you can offer whichever channels you like. You could offer just one channel, a combination of channels, or you could offer all of them. The choice is yours!
If you'd just like to offer email as an add-on then you can just offer email. Likewise, if you wanted to offer a selection of email, SMS, and survey you can offer just these channels. The platform is fully customizable for your needs and your customers' needs.
SimplyCast does their best to keep the reseller portal up to date with the most recent version. At most, resellers will be one version behind, but unless that happens it should be at your discretion if you choose to launch or not launch new channels.