I'm not sure this bug is valid any more. The trusted prompt mechanism is different to how apps are created. Trusted prompts don't have splash screens (maybe they should?), but in any case a trusted session is short-lived, just for the duration of the prompt. The connection to Mir needs to happen on the trusted socket, so there's no connection that could trigger the splash screen (even if there was a splash screen) too early.
I'm not sure this bug is valid any more. The trusted prompt mechanism is different to how apps are created. Trusted prompts don't have splash screens (maybe they should?), but in any case a trusted session is short-lived, just for the duration of the prompt. The connection to Mir needs to happen on the trusted socket, so there's no connection that could trigger the splash screen (even if there was a splash screen) too early.