Agree with all four; I prefer inline expansion to popups as well. Especially 2/ - multiple popups can quickly lead to a mess on screen, just like on the Wikipedia's Navigation Popups screenshot, where it does not only look ugly, but the popups also obscure each other as well as the original text.
Comments
About popups/tooltips/hovercards: I considered this approach, but decided to go with this sort of "inline" expansion for the following reasons:
1. A popup obscures the original text. This interferes with context, albeit admittedly to a much lesser degree than full-blown navigation, but still.
2. Multi-level popup hierarchies just don't look good, in my opinion.
3. You must dismiss a popup to continue, whereas with inline expansion you can just as well keep the expansion and continue reading.
4. The hover approach doesn't work as well for touch-devices (i.e. without a mouse).
Agree with all four; I prefer inline expansion to popups as well. Especially 2/ - multiple popups can quickly lead to a mess on screen, just like on the Wikipedia's Navigation Popups screenshot, where it does not only look ugly, but the popups also obscure each other as well as the original text.