According to their site, they used to support Samsung a long time ago but Samsung made changes in newer handsets that closed off access to the secure element.

Samsung phones and TVs have tons of adware built in. I'm pretty sure they won't want GrapheneOS on their phones. Motorola, on the other hand, has always shipped stock OS with minor customization. The only problem with Motorola is that their support is very short (like 2 years).

That would be entirely up to Samsung. It's not likely.