Having come up against a few problems with exporting vectors to Affinity Designer from V5 / V7, these are a few observations of the clipboard copy/paste function from V8, into AD. I think AD is reading the svg version of what V8 puts on the clipboard, but I’m not certain of that.
Firstly, the copied geometry is not pasted at 1:1. I’m not sure at exactly what scale it is pasted. However, if a bounding box of known dimensions (say A4, 297 x 210) is copied along with what you want to port, then in AD it can all be set to the correct size using the Transform tab - lock the H./W. ratio then type the correct length of one edge.
Colours: A mixed bag. This is Rhino (the colours are a long way off in the screenshot compared to what I’m seeing, but that’s an aside):
The outer black rectangle is the A4 bounding box; set to No Print. The bottom LH corner is at 0,0.
The (blue!?) triangle and fill is on a layer “Blue”, set to Rhino stock palette “Blue”. The triangle is closed (Join)
The green rectangle with radiused corners is on a layer “Cyan”, layer colour Cyan, but display colour for the object is set to Green (all stock Rhino palette colours). The rectangle is closed (Join).
The ellipse and hatch is on a layer “Red”. Both objects have their colour set by layer. Hatch rotation 45 deg, scale 50.
The circle is on a layer “Gold”. Object colour by layer. It’s a Block called “Circle” on layer “Red”.
The black right angle line with filleted corner is on layer on layer Default. Print width is set to 0.5mm (all other objects are default print width). It is not joined. Cap style for the line is the default “Round”.
When I paste this into AD, out of the box I see this:
Sure enough, the bounding box set to No Print means that it doesn’t come through. I have to add that back in to be able to scale everything. But the No Print out of Rhino does indeed mean it won’t port.
With the bounding rectangle reinstated, the long edge length is 195mm; just short of two-thirds what it should be. Line width for the black right angle is shown as 0.5mm. Everything else is 0.4mm. Where is the Rhino V8 setting for default line width? Once everything is scaled up to the correct size, the line widths are unchanged (i.e. they do not scale)
Going through the objects in the same order as listed above:
The blue vector triangle is red. I don’t know where AD got that from? The fill is still blue; RGB values match those in Rhino (RGB 0,0,255). It’s just they look very different in the two softwares. The fill is a good fit to the outline vector and is editable in AD without any further work.
The green rectangle is not closed and it’s cyan, not green. So the layer colour has been read, not the object colour information. Can this be changed so that Rhino copies the object data to svg clipboard, or at least offer the option? And keep Joined objects joined, please?
The corner fillets are tangent! 
. AD isn’t reporting a “radius”, just the bounding box dims… The corner fillet itself is interesting as it doesn’t have the usual four CP’s for a Bezier. AD is reading the (svg?) arc in some way that is closer to an arc. Bounding box 4.2 x 0.9mm. The radius in Rhino was 3.0mm.
The red ellipse also has CP’s that are very similar to what you see in Rhino. It is not made up of four/eight/sixteen Beziers. The hatch lines don’t terminate very neatly where they meet the ellipse. They are individual ojects and they aren’t grouped or combined.
The circle is Gold. So the object layer colour is read, not the layer that the block instance resides on.
The right angle line with fillet also has a tangent fillet. The objects aren’t joined. Line ends terminate with a neat round.
All in all, it’s not quite there but but shows a lot of promise. Is this going to receive further development from McNeel any time soon? If the colour vagaries are sorted and joined vectors could remain joined, it would be very close to a usable tool for everyday work.